Question and Answers
Q.1 What does Moen-Jo-Daro means? Where is it situated?
Ans. Moen-Jo-Daro means “Mound of the Dead”. It is situated at a distance of 27km from Larkana on the right bank of river Indus.
Q.2 Who was Sir John Marshall?
Ans. Sir John Marshall was an English civil servant, whose work was to look after historical remains, like ancient building and other old things such as these pieces of pots and bricks. He was very interested in history and was anxious to find out about these remains.
Q.3 What did Sir John Marshall remark, when pieces of old pots and bricks were brought to him?
Ans. sir John Marshall was an English civil servant who was interested in old historical remains. So when some villagers brought pieces of old pots and bricks he at once know that they were pieces of historical remains.
He remarked that perhaps these was an ancient city lying under the mound of day and sand. He directed the villagers to dig there in the hope that they would uncover the remains of an ancient city.
Q.4 What was the occupations of the people of Moen-Jo-Daro?
Ans. The people of Moen-Jo-Daro were traders. They traded with other cities and traveled from place to place on business.
They were skilled craft men who worked with gold and silver.
They were farmers who grew wheat, rice and cotton and they also kept cattle.
Q.5 How was the city of Moen-Jo-Daro planned?
Ans. The city of Moen-Jo-Daro was a well planned and cleaned city. Each house was made of large baked bricks and a bathroom and servant-quarters close by covered drains beside the streets. The streets were made of baked bricks.
There was a great hall where grain were stored. There is a wide road in the middle of which was the shopping centre with shops on both sides.
Q.6 Name any four objects on exhibition in the Moen-Jo-Daro Museum? or Name any four findings of Moen-Jo-Daro?
Ans. The objects found in Moen-Jo-Daro are:
1. A metal statue of a dancing girl.
2. Seals, Gold, Silver and Ivory Jewelery.
3. Painted Pottery
4. Metal tools and weapons.
5. The head of a bull.
Q.7 How old is the civilization of Moen-Jo-Daro?
Ans. The civilization of Moen-Jo-Daro is 4500 years old.
Q.8 How did this civilization come to an end?
Ans. No body knows exactly how this ancient civilization came to an end. Either they were from the north or some great earthquake destroyed them.
Q.9 How do we know Moen-Jo-Daro’s probable age? What can help us to know more about civilization?
Ans. We know Moen-Jo-Daro’s probable ge from the metal objects found from the execution. We can learn more about this civilization if the language experts are able to determine the meanings of the words written on the seals and the pottery.
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Thursday, June 30, 2011
Class IX, ENGLISH, "The Neem Tree"
Question and Answers
Q.1 How can the Neem Tree prevent the burning heat of the sun from troubling us?
Ans. The high Neem Tree with its extending branches interrupts the scorching heat of the mid day sun and provide soothing shade to people. In this way, it prevents the burning heat of the sun from troubling us.
Q.2 Why does the poetess say that Neem Tree is unafraid?
Ans. The poetess Mrs. Elsa Kazi says that the Neem Tree is unafraid of the burning heat of the sun and stands unprotected and unrefreshed the whole day long in the scorching heat of the sun.
Q.3 What does the Neem Tree look like?
Ans. The Neem Tree looks like a man, facing every fate in life, boldly and bravely.
Q.4 How does the poetess compare the Neem Tree to man?
Ans. The Neem tree provides shelter to people and protects them from the scorching heat of the sun without any protection for itself. It stands out in the open hot sun bearing the fierce heat. In the someway, man can be as fold as the Neem tree and try to protect his fellow human beings from sorrow and poverty by sacrificing his own comfort.
Q.5 What according to the poetess is the highest aim in life?
Ans. A man must hold with determination for all kinds of difficulties in life and accept the ups and downs of life in a stead fast manner. Through self sacrifice he must help his fellow human beings who are poor, sad and in trouble and guide them on the right path. This, according to Mrs. Elsa Kazi is the highest aim of the life.
Q.1 How can the Neem Tree prevent the burning heat of the sun from troubling us?
Ans. The high Neem Tree with its extending branches interrupts the scorching heat of the mid day sun and provide soothing shade to people. In this way, it prevents the burning heat of the sun from troubling us.
Q.2 Why does the poetess say that Neem Tree is unafraid?
Ans. The poetess Mrs. Elsa Kazi says that the Neem Tree is unafraid of the burning heat of the sun and stands unprotected and unrefreshed the whole day long in the scorching heat of the sun.
Q.3 What does the Neem Tree look like?
Ans. The Neem Tree looks like a man, facing every fate in life, boldly and bravely.
Q.4 How does the poetess compare the Neem Tree to man?
Ans. The Neem tree provides shelter to people and protects them from the scorching heat of the sun without any protection for itself. It stands out in the open hot sun bearing the fierce heat. In the someway, man can be as fold as the Neem tree and try to protect his fellow human beings from sorrow and poverty by sacrificing his own comfort.
Q.5 What according to the poetess is the highest aim in life?
Ans. A man must hold with determination for all kinds of difficulties in life and accept the ups and downs of life in a stead fast manner. Through self sacrifice he must help his fellow human beings who are poor, sad and in trouble and guide them on the right path. This, according to Mrs. Elsa Kazi is the highest aim of the life.
Class IX, ENGLISH, "Shah Abdul Latif"
Question and Answers
Q.1 Who was Shah Abdul Latif? Where and when was he born?
Ans. Shah Abdul Latif was a great saint who is lovingly called “Lal Latif” by his devotees. He was born in a small village called “Hala Haveli” in the year 1689.
Q.2 What do you know about the ancestors of Shah Abdul Latif?
Ans. Shah Abdul Latif’s ancestors had migrated to Sindh during the days of Tamerlane. They had come from Hiirat a town in West Afghanistan. They liked Sindh so much so that they decided to make it their permanent home. Many centuries later one of their decendants, Syed Habib Shah, was blessed with a son who grew up to be “Saint Lal Latif”.
Q.3 Why is Shah Latif known as “Saint of Bhit”?
Ans. When Shah Latif father died, he left his home and went to live on a Mound at some distance from his village. A mound of sand is called “Bhit” in Sindhi. Due to the fact that he lived on this mound for the rest of his life, Shah Latif came to be known as “The Saint of Bhit.”
Q.4 Name the shrines of saints found in Pakistan.
Ans. In every part of our country, there are shrines of such saints:
In Lahore, The shrines of Data Ganj Bakhsh and Mian Mir Sahib.
In Pak Pattan, Lived and Died Baba Fareed.
In Multan, The Shrine of Ghoues Bahaul Haq.
In Sindh, the Shrines of Shah Abdul Latif and Qalander Lal Shahbaz.
In Peshawar, in Quetta, and in countless other towns and cities there are the tombs of these man of God.
Q.5 What are the important features of Shah Latif poetry?
Ans. The important features of Shah Latif’s poetry is that it is written in the language of the common people, and other great quality of his poetry beside its simplicity is its moving music.
Q.6 What is the message of Shah Latif’s poetry? or What according Shah Latif is the goal of life?
Ans. The message of Shah Latif is the message of love. He believed in the brotherhood and equality of men and in pleasing God by good deeds. This according to Shah Latif is the goal of life.
Q.7 When is the Urs of Shah Abdul Latif’s held?
Ans. Shah Abdul Latif Urs is held at his shrine every year on 14th Safar, the second, month of the muslim calender.
Q.8 How do Shah Latif’s devotees celebrate his Urs?
Ans. Shah Latif’s Urs is held at his shrine every year in 14th Safar, the second month of the Muslim calender. Thousands of people gather to listen to the Saint’s song sung to the Tambooro and after their prayers. Many learned men read papers that tell about Latif’s life and poetry.
Q.9 What do you know about Shah Latif’s music?
Ans. Shah Latif was not only a saint and a poet but also a great musician. He found great comfort in music. His skill in this art enabled him to make many improvements and changes in the difficult music of his time. He loved simplicity in music and musical instruments. He did not agree with the idea that music should be difficult. So he made it simple and also vented on instrument called “Tambooro”.
Q.10 What do you know about Tamboora?
Ans. The tambooro is a simple musical instrument invented by the Sufi, philosopher Shah Abdul Latif.
Q.11 Write a short note on the poetry of Shah Abdul Latif?
Ans. Shah Abdul Latif started composing poetry while he was only a boy. Shah Abdul Latif was a mystic poet. He was a versatile, genious and had attempted all aspects of poetry.
Shah Abdul Latif was a poet of the people and was successful in awakening them to the discovery of the truth of spiritual life. He had very deed sympathy for the poor and had expressed in his sentiments about them with great pathos and fubings.
His collection of poems was so valued that it was translated into many languages and is called “Risalo of Shah Latif.”
Q.1 Who was Shah Abdul Latif? Where and when was he born?
Ans. Shah Abdul Latif was a great saint who is lovingly called “Lal Latif” by his devotees. He was born in a small village called “Hala Haveli” in the year 1689.
Q.2 What do you know about the ancestors of Shah Abdul Latif?
Ans. Shah Abdul Latif’s ancestors had migrated to Sindh during the days of Tamerlane. They had come from Hiirat a town in West Afghanistan. They liked Sindh so much so that they decided to make it their permanent home. Many centuries later one of their decendants, Syed Habib Shah, was blessed with a son who grew up to be “Saint Lal Latif”.
Q.3 Why is Shah Latif known as “Saint of Bhit”?
Ans. When Shah Latif father died, he left his home and went to live on a Mound at some distance from his village. A mound of sand is called “Bhit” in Sindhi. Due to the fact that he lived on this mound for the rest of his life, Shah Latif came to be known as “The Saint of Bhit.”
Q.4 Name the shrines of saints found in Pakistan.
Ans. In every part of our country, there are shrines of such saints:
In Lahore, The shrines of Data Ganj Bakhsh and Mian Mir Sahib.
In Pak Pattan, Lived and Died Baba Fareed.
In Multan, The Shrine of Ghoues Bahaul Haq.
In Sindh, the Shrines of Shah Abdul Latif and Qalander Lal Shahbaz.
In Peshawar, in Quetta, and in countless other towns and cities there are the tombs of these man of God.
Q.5 What are the important features of Shah Latif poetry?
Ans. The important features of Shah Latif’s poetry is that it is written in the language of the common people, and other great quality of his poetry beside its simplicity is its moving music.
Q.6 What is the message of Shah Latif’s poetry? or What according Shah Latif is the goal of life?
Ans. The message of Shah Latif is the message of love. He believed in the brotherhood and equality of men and in pleasing God by good deeds. This according to Shah Latif is the goal of life.
Q.7 When is the Urs of Shah Abdul Latif’s held?
Ans. Shah Abdul Latif Urs is held at his shrine every year on 14th Safar, the second, month of the muslim calender.
Q.8 How do Shah Latif’s devotees celebrate his Urs?
Ans. Shah Latif’s Urs is held at his shrine every year in 14th Safar, the second month of the Muslim calender. Thousands of people gather to listen to the Saint’s song sung to the Tambooro and after their prayers. Many learned men read papers that tell about Latif’s life and poetry.
Q.9 What do you know about Shah Latif’s music?
Ans. Shah Latif was not only a saint and a poet but also a great musician. He found great comfort in music. His skill in this art enabled him to make many improvements and changes in the difficult music of his time. He loved simplicity in music and musical instruments. He did not agree with the idea that music should be difficult. So he made it simple and also vented on instrument called “Tambooro”.
Q.10 What do you know about Tamboora?
Ans. The tambooro is a simple musical instrument invented by the Sufi, philosopher Shah Abdul Latif.
Q.11 Write a short note on the poetry of Shah Abdul Latif?
Ans. Shah Abdul Latif started composing poetry while he was only a boy. Shah Abdul Latif was a mystic poet. He was a versatile, genious and had attempted all aspects of poetry.
Shah Abdul Latif was a poet of the people and was successful in awakening them to the discovery of the truth of spiritual life. He had very deed sympathy for the poor and had expressed in his sentiments about them with great pathos and fubings.
His collection of poems was so valued that it was translated into many languages and is called “Risalo of Shah Latif.”
Class IX, ENGLISH, "The Last Sermon of the Holy Prophet (P.B.U.H)"
Question and Answers
Q.1 When and where was Prophet Mohammad (P.B.U.H) born?
Ans. Hazrat Mohammad (P.B.U.H) the prophet of Islam was born in the year 571 A.D at Makkah.
Q.2 To which tribe did Prophet Mohammad belong? What did they believe in?
Ans. Prophet Mohammad belonged to the noble family of Quraish. They believed and worshiped idols and did not believe in one God.
Q.3 What did Prophet Mohammad (P.B.U.H) ask the Quraish to do?
Ans. Hazrat Mohammad (P.B.U.H) asked the Quraish not to worship their false Gods and asked them to worship the one and the only true God.
Q.4 Why did Prophet Mohammad (P.B.U.H) migrate to Madina?
Ans. Most of the people of Makkah refused to accept Islam. They opposed the new faith and their bitter opposition cause the Prophet (P.B.U.H) much agony and a lot of trouble. So in 622 A.D. Prophet Mohammad (P.B.U.H) migrated to Madina.
Q.5 What is Hijra? Where did it take place?
Ans. In 622 A.D the prophet Mohammad (P.B.U.H) accompanied by his faithfully friend Hazrat Abu Bakr migrated to Madina. This count is known in history as the “Hijra”.
Q.6 On what principles was the Islamic Society founded?
Ans. In Madina the Prophet (P.B.U.H) founded the Islamic Society based on the three principles:
* All power belongs to Allah.
* Mohammad (P.B.U.H) is his Prophet.
* All Muslims are brothers to one another.
Q.7 What does the last sermon teach us?
Ans. In the 10th year of Hijra the Prophet (P.B.U.H) together with his followers went to perform Hajj at Makkah. There he addressed a very large gathering of muslims at mount Aarafat. This was the last sermon of the Holy Prophet (P.B.U.H).
It teaches us that there is no God Except Allah. Only the goodness of a person makes him superior to others. The most righteous is the most honourable. All Muslims are brother to one another. Finnally the last sermon teaches us that the Holy Quran is the message of Allah and if we act according to its teachings, we will never go wrong.
Q.8 Why did the Quraish oppose the Holy Prophet (P.B.U.H)?
Ans. The Holy Prophet asked the Quraish not to worship there false Gods but to worship the One and only true God and to accept him as the Prophet of God. However, they refuse to do so and believe that he was preaching against their Gods, and their ancestors. So they oppose the new religion of Islam and their fierce and terrible oppositions made it impossible for the Prophet (P.B.U.H) to continue being in Makkah and compelled him to leave that city, Makkah.
Q.1 When and where was Prophet Mohammad (P.B.U.H) born?
Ans. Hazrat Mohammad (P.B.U.H) the prophet of Islam was born in the year 571 A.D at Makkah.
Q.2 To which tribe did Prophet Mohammad belong? What did they believe in?
Ans. Prophet Mohammad belonged to the noble family of Quraish. They believed and worshiped idols and did not believe in one God.
Q.3 What did Prophet Mohammad (P.B.U.H) ask the Quraish to do?
Ans. Hazrat Mohammad (P.B.U.H) asked the Quraish not to worship their false Gods and asked them to worship the one and the only true God.
Q.4 Why did Prophet Mohammad (P.B.U.H) migrate to Madina?
Ans. Most of the people of Makkah refused to accept Islam. They opposed the new faith and their bitter opposition cause the Prophet (P.B.U.H) much agony and a lot of trouble. So in 622 A.D. Prophet Mohammad (P.B.U.H) migrated to Madina.
Q.5 What is Hijra? Where did it take place?
Ans. In 622 A.D the prophet Mohammad (P.B.U.H) accompanied by his faithfully friend Hazrat Abu Bakr migrated to Madina. This count is known in history as the “Hijra”.
Q.6 On what principles was the Islamic Society founded?
Ans. In Madina the Prophet (P.B.U.H) founded the Islamic Society based on the three principles:
* All power belongs to Allah.
* Mohammad (P.B.U.H) is his Prophet.
* All Muslims are brothers to one another.
Q.7 What does the last sermon teach us?
Ans. In the 10th year of Hijra the Prophet (P.B.U.H) together with his followers went to perform Hajj at Makkah. There he addressed a very large gathering of muslims at mount Aarafat. This was the last sermon of the Holy Prophet (P.B.U.H).
It teaches us that there is no God Except Allah. Only the goodness of a person makes him superior to others. The most righteous is the most honourable. All Muslims are brother to one another. Finnally the last sermon teaches us that the Holy Quran is the message of Allah and if we act according to its teachings, we will never go wrong.
Q.8 Why did the Quraish oppose the Holy Prophet (P.B.U.H)?
Ans. The Holy Prophet asked the Quraish not to worship there false Gods but to worship the One and only true God and to accept him as the Prophet of God. However, they refuse to do so and believe that he was preaching against their Gods, and their ancestors. So they oppose the new religion of Islam and their fierce and terrible oppositions made it impossible for the Prophet (P.B.U.H) to continue being in Makkah and compelled him to leave that city, Makkah.
Class IX, CHEMISTRY, "Differences"
Metals and Non Metals
Metals
1. Metals have luster shine surface.
2. Metals reflect heat and light.
3. Metals conduct heat and electricity
4. Metals are ductile and can be drawn into wire.
Non-Metals
1. Non-Metals have no luster.
2. Non-Metals usually don’t reflect heat and light.
3. Non-Metals do not conduct heat and electricity.
4. Non-Metals are non ductile and cannot be drawn into wire.
5. Non-Metals are non-malleable and can not form sheets.
Homogeneous and Heterogeneous Mixture
Homogeneous Mixture
1. Those mixtures, which have uniform composition throughout their mass are called homogeneous mixtures.
2. Homogeneous mixture has only one phase through out its mass.
3. Homogeneous mixture are also known as solution.
4. Examples: Salt and water, Sugar and water.
Heterogeneous Mixture
1. Those mixtures, which do not have uniform composition through their mass are called Heterogeneous Mixture.
2. Heterogeneous Mixture has more than one phase through out its mass.
3. Heterogeneous Mixture are not solutions.
4. Examples: Rocks, Soil, Food products.
Molecular and Empirical Formula
Molecular Formula
1. Formula which shows the actual number of atoms of each element present in a molecule is called Molecular Formula.
2. Molecular Formula shows the structure of compound.
3. Two or more compounds cannot have same Molecular Formula.
4. Molecular Formula = n x Empirical Formula.
5. It represents covalent compounds only.
Empirical Formula
1. formula, which shows the relative ratio of atoms of each element present in a molecule, is called Empirical Formula.
2. Empirical Formula can not show the structure of compound.
3. Two or more compounds can have same Empirical Formula.
4. Empirical Formula = Molecular Formula / n
5. It represent an ionic compound as well as a covalent compound.
Symbol and Formula
Symbol
1. A symbol is an abbreviation for the chemical name of an element and represents only one atom of the element.
2. It represents one atom of an element.
3. Symbol is written for elements.
4. Examples: Na, Br, Cl, F etc.
Formula
1. Representation of compound in terms of symbols is called formula. It represents one atom of an element.
2. It represents atoms of same or different elements present in one molecule.
3. It represents an ionic compounds as well as a covalent compound.
4. Examples: H2O, NH3 etc.
Gram and Gram Molecule
Gram
The atomic mass of an element expressed in grams is called gram atomic mass.
2. It is associated with element only.
3. It is the mass of one atomic mole.
4. One gram atom of any substance contains 6.02 x 10(23) atoms. (23 is the power of 10).
Gram Molecule
1. Molecular mass of any element or compound expressed in grams is called gram molecule.
2. It is associated with element and compound.
3. It is the mass of one molecular mole.
4. One gram molecule of any substance contains 6.02 x 10(23) atoms. (23 is the power of 10).
Atom and Molecule
Atom
1. It is the smallest particle of an element which can enter into a chemical reaction.
2. It is represented by a symbol of the element.
3. It shows the properties of the element.
4. It retains its identity in a chemical reaction.
Molecule
1. It is the smallest particle of a substance which can exist and show all the properties of the substance.
2. It is represented by a molecular formula of the substance.
3. It shows the properties of the substance.
4. It does not retain its identity in a chemical reaction.
Exothermic and Endothermic Reactions
Exothermic Reaction
1. Those chemical reactions in which heat energy is evolved are called exothermic reactions.
2. In exothermic reactions the enthalpy of products is lower than the reactants. H is therefore negative for an exothermic reaction.
3. During endothermic reaction, the system becomes colder and net potential energy of substance increases.
4. The energy is absorbed during these reactions.
5. The temperature of reaction therefore decreases.
Endothermic Reactions
1. Those chemical reactions in which heat energy is absorbed are called endothermic reactions.
2. In endothermic reactions the enthalpy of reactants is lower than the products. H is therefore positive in endothermic reaction.
3. During endothermic reaction, the system becomes colder and net potential energy of substance increases.
4. The energy is absorbed during these reactions.
5. The temperature of reaction therefore decreases.
Physical and Chemical Properties
Physical Properties
1. The physical properties of a substance are those characteristics which serve to distinguish it from other substance but do not deal with its ability to undergo chemical changes.
2. These are related to the physical state of matter.
3. Examples: Formation of ice from water, formation of a magnet from ice etc.
Chemical Properties
1. The chemical properties of a substance indicate the ability of a substance to undergo chemical changes.
2. They are related to the chemical change of a substance.
3. Examples: burning of paper, rusting of iron.
Electrolyte and Non-Electrolyte
Electrolytes
1. Electrolytes conduct electricity in molten or in solution form.
2. These form positive and negative ions when dissolved in water e.g. NaCl form Na+ and Cl- ions when dissolved in water.
3. Chemical changes occur when electric current is passed through the electrolyte.
4. Generally these are ionic or polar covalent compounds.
Non-Electrolytes
1. Non-electrolytes do not conduct electric current in molten or in solution form.
2. These do not form positive and negative ions when dissolved in water e.g. Urea, sugar, glucose etc.
2. No chemical change occurs in them on passing current.
3. Generally these are non polar covalent compounds.
4. Generally these are non polar covalent compounds.
Acid and Base
Acid
1. Those compounds which provide hydrogen ion (H+) in aqueous solutions are called Acids.
2. An acid is a substance which produces H+ ions in aqueous solution.
3. Acid is a species (a compound or ion) which donates or tends to donate a proton (H+).
4. An acid is a species (molecule or ion) which can accept a pair of electron. An acid is also called an electrophile (electron loving).
5. They have sour taste.
6. Acid turn blue litmus red methyl orange red.
Base
1. Those compounds, which provides hydroxyl (OH-) ion in aqueous solution, are called bases.
2. A base is a substance, which gives (OH-) in aqueous solution.
3. A base is a species, which accepts or tends to accept a proton.
4. A base is a species (molecule or ion) which can donate a pair of electrons. A base is also called a nucleophile (Nucleus loving).
5. Bases have bitter taste.
6. Bases turn red litmus to blue, colorless phenolphthalein to pink and methyl orange to yellow.
Ionic and Covalent Bond
Ionic Bond
1. Ionic bond is formed by complete transfer of electrons from one atom to another atom.
2. Ionic bond is always formed between different atoms. E.g. NaCl, CaCl2.
3. In ionic bond atoms have very large electro-negativity and ionization energy difference.
4. This bond is usually formed between metals and non-metals.
5. This bond is very strong.
6. As a result of this bond ionic compounds are formed.
7. It is always formed between two different atoms.
8. It is formed when difference of electro-negativity of combining atoms is 1.7 or more.
Covalent Bond
1. Covalent bond is formed by the mutual sharing of electrons between two atoms.
2. Covalent bond may be formed between similar or dissimilar atoms e.g. H2, O2, HCl etc.
3. In covalent bond atoms have very small electro-negativity or ionization energy difference.
4. This bond is usually formed between non-metals only.
5. This bond is comparatively less strong.
6. As a result of this bond covalent compounds are formed.
7. It is formed between similar and different types of atoms.
8. It is formed when difference of electro-negativity of combining atoms is less than 1.7.
Ionic and Covalent Compounds
Ionic Compounds
1. The ionic compounds are usually solid, hard and brittle.
2. The ionic compounds are good conductors of electricity either in fused state or in the form of aqueous solution.
3. Ionic Compounds have high melting points and boiling points.
4. Ionic compounds have high melting points and boiling points.
5. Covalent compounds are mostly volatile.
Covalent Compounds
1. Covalent compounds exist in all the three states i.e. gas, liquid and solid.
2. A pure covalent compound does not conduct electricity.
3. These have usually low melting and boiling points.
4. These are soluble in water.
5. These are insoluble in water but soluble in organic solvents.
Co-Ordinate Covalent and Covalent Bond
Co-Ordinate Covalent Bond
1. It is a bond in which the shared electron pair is denoted by one atom only.
2. One atom donates electrons but other has no contribution.
3. Lewis acids and bases always from this bond.
4. It is represented by ->.
5. It is formed by the donation of an electron apir by one of the two bonded atoms.
6. It is formed by the completely filled atomic orbital.
Covalent Bond
1. It is a bond formed by the mutual sharing of electrons.
2. In the shared electron pair both atoms have equal contribution.
3. Lewis acids and bases do not form this bond.
4. It is represented by _.
5. It is formed by the mutual sharing of electrons between atoms.
6. It is formed by the overlap of partially filled atomic orbital.
Polar and Non-Polar Covalent Bond
Polar Covalent Bond
1. The covalent bond between two atoms having different electro-negativity is called a polar covalent bond.
2. In a polar bond, the shared electron pair is not equally attracted by the bonded atoms.
3. Bonded atoms become slightly charged and acquire partial =ve and -ve charges.
4. It has an ionic character.
5. The bond energy is greater.
Non-Polar Covalent Bond
1. The covalent bond between two atoms having same electro-negativity is called a non-polar covalent bond.
2. In a non polar bond, the shared electron pair is equally attracted by the bonded atoms.
3. Bonded atoms remain electrically neutral and do not acquire partial charges.
4. It has no ionic character.
5. The bond energy is lesser.
Electrolytic and Galvanic or Voltaic Cell
Electrolytic Cell
1. It is a device for converting electrical energy into chemical energy. It means by passing current through an electrolyte, chemical reaction takes place.
2. It consists of a vessel containing an electrodes and a source of direct current (battery).
3. Example: Electrolysis of aqueous solution of NaCl.
Galvanic or Voltaic Cell
1. It is a device for converting chemical energy into electrical energy. It means spontaneous redox reaction is used for the production of electric current. This cell was prepared by L.Galvani and A.Volts, hence named as Galvanic or Voltaic Cell.
2. It consists of two half-cells. Each half cell consists of an electrodes and the solution with which it is in contact.
3. Example: Daniel Cell-Zn/ZnSO4 and Cu/CuSO4 cell.
Solution and Suspension
Solution
The size of particles is between 0.1 to 1nm.
2. Particles cannot be seen with low power microscope.
3. It is homogeneous.
4. Particles do not settle down.
5. It is transparent.
6. Components cannot be separated by filtration.
Suspension
1. The size of particles is larger than 1000nm.
2. Particles can be seen by low power microscope.
3. It is heterogeneous.
4. Particles settle down.
5. It is not transparent.
6. Components can be separated by filtration.
Metals
1. Metals have luster shine surface.
2. Metals reflect heat and light.
3. Metals conduct heat and electricity
4. Metals are ductile and can be drawn into wire.
Non-Metals
1. Non-Metals have no luster.
2. Non-Metals usually don’t reflect heat and light.
3. Non-Metals do not conduct heat and electricity.
4. Non-Metals are non ductile and cannot be drawn into wire.
5. Non-Metals are non-malleable and can not form sheets.
Homogeneous and Heterogeneous Mixture
Homogeneous Mixture
1. Those mixtures, which have uniform composition throughout their mass are called homogeneous mixtures.
2. Homogeneous mixture has only one phase through out its mass.
3. Homogeneous mixture are also known as solution.
4. Examples: Salt and water, Sugar and water.
Heterogeneous Mixture
1. Those mixtures, which do not have uniform composition through their mass are called Heterogeneous Mixture.
2. Heterogeneous Mixture has more than one phase through out its mass.
3. Heterogeneous Mixture are not solutions.
4. Examples: Rocks, Soil, Food products.
Molecular and Empirical Formula
Molecular Formula
1. Formula which shows the actual number of atoms of each element present in a molecule is called Molecular Formula.
2. Molecular Formula shows the structure of compound.
3. Two or more compounds cannot have same Molecular Formula.
4. Molecular Formula = n x Empirical Formula.
5. It represents covalent compounds only.
Empirical Formula
1. formula, which shows the relative ratio of atoms of each element present in a molecule, is called Empirical Formula.
2. Empirical Formula can not show the structure of compound.
3. Two or more compounds can have same Empirical Formula.
4. Empirical Formula = Molecular Formula / n
5. It represent an ionic compound as well as a covalent compound.
Symbol and Formula
Symbol
1. A symbol is an abbreviation for the chemical name of an element and represents only one atom of the element.
2. It represents one atom of an element.
3. Symbol is written for elements.
4. Examples: Na, Br, Cl, F etc.
Formula
1. Representation of compound in terms of symbols is called formula. It represents one atom of an element.
2. It represents atoms of same or different elements present in one molecule.
3. It represents an ionic compounds as well as a covalent compound.
4. Examples: H2O, NH3 etc.
Gram and Gram Molecule
Gram
The atomic mass of an element expressed in grams is called gram atomic mass.
2. It is associated with element only.
3. It is the mass of one atomic mole.
4. One gram atom of any substance contains 6.02 x 10(23) atoms. (23 is the power of 10).
Gram Molecule
1. Molecular mass of any element or compound expressed in grams is called gram molecule.
2. It is associated with element and compound.
3. It is the mass of one molecular mole.
4. One gram molecule of any substance contains 6.02 x 10(23) atoms. (23 is the power of 10).
Atom and Molecule
Atom
1. It is the smallest particle of an element which can enter into a chemical reaction.
2. It is represented by a symbol of the element.
3. It shows the properties of the element.
4. It retains its identity in a chemical reaction.
Molecule
1. It is the smallest particle of a substance which can exist and show all the properties of the substance.
2. It is represented by a molecular formula of the substance.
3. It shows the properties of the substance.
4. It does not retain its identity in a chemical reaction.
Exothermic and Endothermic Reactions
Exothermic Reaction
1. Those chemical reactions in which heat energy is evolved are called exothermic reactions.
2. In exothermic reactions the enthalpy of products is lower than the reactants. H is therefore negative for an exothermic reaction.
3. During endothermic reaction, the system becomes colder and net potential energy of substance increases.
4. The energy is absorbed during these reactions.
5. The temperature of reaction therefore decreases.
Endothermic Reactions
1. Those chemical reactions in which heat energy is absorbed are called endothermic reactions.
2. In endothermic reactions the enthalpy of reactants is lower than the products. H is therefore positive in endothermic reaction.
3. During endothermic reaction, the system becomes colder and net potential energy of substance increases.
4. The energy is absorbed during these reactions.
5. The temperature of reaction therefore decreases.
Physical and Chemical Properties
Physical Properties
1. The physical properties of a substance are those characteristics which serve to distinguish it from other substance but do not deal with its ability to undergo chemical changes.
2. These are related to the physical state of matter.
3. Examples: Formation of ice from water, formation of a magnet from ice etc.
Chemical Properties
1. The chemical properties of a substance indicate the ability of a substance to undergo chemical changes.
2. They are related to the chemical change of a substance.
3. Examples: burning of paper, rusting of iron.
Electrolyte and Non-Electrolyte
Electrolytes
1. Electrolytes conduct electricity in molten or in solution form.
2. These form positive and negative ions when dissolved in water e.g. NaCl form Na+ and Cl- ions when dissolved in water.
3. Chemical changes occur when electric current is passed through the electrolyte.
4. Generally these are ionic or polar covalent compounds.
Non-Electrolytes
1. Non-electrolytes do not conduct electric current in molten or in solution form.
2. These do not form positive and negative ions when dissolved in water e.g. Urea, sugar, glucose etc.
2. No chemical change occurs in them on passing current.
3. Generally these are non polar covalent compounds.
4. Generally these are non polar covalent compounds.
Acid and Base
Acid
1. Those compounds which provide hydrogen ion (H+) in aqueous solutions are called Acids.
2. An acid is a substance which produces H+ ions in aqueous solution.
3. Acid is a species (a compound or ion) which donates or tends to donate a proton (H+).
4. An acid is a species (molecule or ion) which can accept a pair of electron. An acid is also called an electrophile (electron loving).
5. They have sour taste.
6. Acid turn blue litmus red methyl orange red.
Base
1. Those compounds, which provides hydroxyl (OH-) ion in aqueous solution, are called bases.
2. A base is a substance, which gives (OH-) in aqueous solution.
3. A base is a species, which accepts or tends to accept a proton.
4. A base is a species (molecule or ion) which can donate a pair of electrons. A base is also called a nucleophile (Nucleus loving).
5. Bases have bitter taste.
6. Bases turn red litmus to blue, colorless phenolphthalein to pink and methyl orange to yellow.
Ionic and Covalent Bond
Ionic Bond
1. Ionic bond is formed by complete transfer of electrons from one atom to another atom.
2. Ionic bond is always formed between different atoms. E.g. NaCl, CaCl2.
3. In ionic bond atoms have very large electro-negativity and ionization energy difference.
4. This bond is usually formed between metals and non-metals.
5. This bond is very strong.
6. As a result of this bond ionic compounds are formed.
7. It is always formed between two different atoms.
8. It is formed when difference of electro-negativity of combining atoms is 1.7 or more.
Covalent Bond
1. Covalent bond is formed by the mutual sharing of electrons between two atoms.
2. Covalent bond may be formed between similar or dissimilar atoms e.g. H2, O2, HCl etc.
3. In covalent bond atoms have very small electro-negativity or ionization energy difference.
4. This bond is usually formed between non-metals only.
5. This bond is comparatively less strong.
6. As a result of this bond covalent compounds are formed.
7. It is formed between similar and different types of atoms.
8. It is formed when difference of electro-negativity of combining atoms is less than 1.7.
Ionic and Covalent Compounds
Ionic Compounds
1. The ionic compounds are usually solid, hard and brittle.
2. The ionic compounds are good conductors of electricity either in fused state or in the form of aqueous solution.
3. Ionic Compounds have high melting points and boiling points.
4. Ionic compounds have high melting points and boiling points.
5. Covalent compounds are mostly volatile.
Covalent Compounds
1. Covalent compounds exist in all the three states i.e. gas, liquid and solid.
2. A pure covalent compound does not conduct electricity.
3. These have usually low melting and boiling points.
4. These are soluble in water.
5. These are insoluble in water but soluble in organic solvents.
Co-Ordinate Covalent and Covalent Bond
Co-Ordinate Covalent Bond
1. It is a bond in which the shared electron pair is denoted by one atom only.
2. One atom donates electrons but other has no contribution.
3. Lewis acids and bases always from this bond.
4. It is represented by ->.
5. It is formed by the donation of an electron apir by one of the two bonded atoms.
6. It is formed by the completely filled atomic orbital.
Covalent Bond
1. It is a bond formed by the mutual sharing of electrons.
2. In the shared electron pair both atoms have equal contribution.
3. Lewis acids and bases do not form this bond.
4. It is represented by _.
5. It is formed by the mutual sharing of electrons between atoms.
6. It is formed by the overlap of partially filled atomic orbital.
Polar and Non-Polar Covalent Bond
Polar Covalent Bond
1. The covalent bond between two atoms having different electro-negativity is called a polar covalent bond.
2. In a polar bond, the shared electron pair is not equally attracted by the bonded atoms.
3. Bonded atoms become slightly charged and acquire partial =ve and -ve charges.
4. It has an ionic character.
5. The bond energy is greater.
Non-Polar Covalent Bond
1. The covalent bond between two atoms having same electro-negativity is called a non-polar covalent bond.
2. In a non polar bond, the shared electron pair is equally attracted by the bonded atoms.
3. Bonded atoms remain electrically neutral and do not acquire partial charges.
4. It has no ionic character.
5. The bond energy is lesser.
Electrolytic and Galvanic or Voltaic Cell
Electrolytic Cell
1. It is a device for converting electrical energy into chemical energy. It means by passing current through an electrolyte, chemical reaction takes place.
2. It consists of a vessel containing an electrodes and a source of direct current (battery).
3. Example: Electrolysis of aqueous solution of NaCl.
Galvanic or Voltaic Cell
1. It is a device for converting chemical energy into electrical energy. It means spontaneous redox reaction is used for the production of electric current. This cell was prepared by L.Galvani and A.Volts, hence named as Galvanic or Voltaic Cell.
2. It consists of two half-cells. Each half cell consists of an electrodes and the solution with which it is in contact.
3. Example: Daniel Cell-Zn/ZnSO4 and Cu/CuSO4 cell.
Solution and Suspension
Solution
The size of particles is between 0.1 to 1nm.
2. Particles cannot be seen with low power microscope.
3. It is homogeneous.
4. Particles do not settle down.
5. It is transparent.
6. Components cannot be separated by filtration.
Suspension
1. The size of particles is larger than 1000nm.
2. Particles can be seen by low power microscope.
3. It is heterogeneous.
4. Particles settle down.
5. It is not transparent.
6. Components can be separated by filtration.
Class IX, CHEMISTRY, "Electro-Chemistry"
Electro-Chemistry
The branch of chemistry which deals with the study of chemical energy to electrical energy or electrical energy to chemical energy is called electro-chemistry.
Conductors
Those substances through which electric current can pass are called conductors. For example all metals are conductors.
Non-Conductors
Those substances through which electric current cannot pass are called non-conductors. For example plastic, wood are non-conductors.
Electrolysis
The process in which electricity passes through the aqueous or infused state of some substance. The substances itself decompose into its component. This process is called electrolysis.
Electrolyte
The compound in molten state or in aqueous solution through which electricity can pass are called electrolyte.
Non-Electrolyte
Those compounds through which electricity cannot pass are called non-electrolyte.
Strong Electrolyte
The substances which are highly soluble and completely ionized are called strong electrolyte. For example acids, bases and salts are strong electrolytes.
Weak Electrolyte
The substances which are not highly soluble and remain in un-ionized form are called weak electrolyte.
Electroplating
A process in which metal is deposited on the surface of another metal by electrolysis is called electroplating.
Objectives of Electroplating
Decoration
It is done for decoration. Noble and precious metals like gold or silver are deposited on the inferior metals to enhance their beauty and look beautiful.
Protection
Electroplating is done to protect the metals from rusting as well as from attack of other substance like organic acids and acidic gases.
Repair
It can be used to repair the broken machinery by electroplating with other metals. Usually the metals like copper, silver, chromium, nickel and gold are used for electroplating.
Procedure of Electroplating
The metal which is to be electroplated is first cleaned with sand and then washed with caustic soda solution and finally with a lot of water.
This metal is made cathode and the metal which is going to be deposited is made anode. The electrolyte is a salt of metal being deposited and electroplating is carried out in a tank made of cement, glass or wood. It is called an electrolytic tank.
The electrolyte should have following properties:
1. It must be very soluble in water.
2. It must be good conductor.
3. Cheap
4. May not easily oxidized or reduced or hydrolyzed.
(Diagram)
The branch of chemistry which deals with the study of chemical energy to electrical energy or electrical energy to chemical energy is called electro-chemistry.
Conductors
Those substances through which electric current can pass are called conductors. For example all metals are conductors.
Non-Conductors
Those substances through which electric current cannot pass are called non-conductors. For example plastic, wood are non-conductors.
Electrolysis
The process in which electricity passes through the aqueous or infused state of some substance. The substances itself decompose into its component. This process is called electrolysis.
Electrolyte
The compound in molten state or in aqueous solution through which electricity can pass are called electrolyte.
Non-Electrolyte
Those compounds through which electricity cannot pass are called non-electrolyte.
Strong Electrolyte
The substances which are highly soluble and completely ionized are called strong electrolyte. For example acids, bases and salts are strong electrolytes.
Weak Electrolyte
The substances which are not highly soluble and remain in un-ionized form are called weak electrolyte.
Electroplating
A process in which metal is deposited on the surface of another metal by electrolysis is called electroplating.
Objectives of Electroplating
Decoration
It is done for decoration. Noble and precious metals like gold or silver are deposited on the inferior metals to enhance their beauty and look beautiful.
Protection
Electroplating is done to protect the metals from rusting as well as from attack of other substance like organic acids and acidic gases.
Repair
It can be used to repair the broken machinery by electroplating with other metals. Usually the metals like copper, silver, chromium, nickel and gold are used for electroplating.
Procedure of Electroplating
The metal which is to be electroplated is first cleaned with sand and then washed with caustic soda solution and finally with a lot of water.
This metal is made cathode and the metal which is going to be deposited is made anode. The electrolyte is a salt of metal being deposited and electroplating is carried out in a tank made of cement, glass or wood. It is called an electrolytic tank.
The electrolyte should have following properties:
1. It must be very soluble in water.
2. It must be good conductor.
3. Cheap
4. May not easily oxidized or reduced or hydrolyzed.
(Diagram)
Class IX, CHEMISTRY, "Solution and Suspension"
Solution
A homogeneous mixture of different chemical substances which has uniform chemical composition through out and shows uniform physical properties is called solution. For example dissolve a small amount of copper sulphate in water the water will become blue. If this blue liquid is filtered, it will pass through the filter paper without leaving any solid. The mixture thus prepared is called a solution.
Binary Solution
A solution which is formed by mixing two substances is called binary solution. For example solution of glucose and water.
Solute
The component of a binary solution which is in lesser amount is called solute. For example in copper sulphate solution, copper sulphate is solute.
Solvent
The component of a binary solution which is in greater amount is called solvent. For example in copper sulphate solution, water is solvent.
Saturated solution
A solution in which maximum amount of a solute has been dissolved at a particular temperature and in which the dissolved form of solute is at equilibrium with its undissolved form is called saturated solution.
Unsaturated Solution
Solution which can dissolve further amount of a solute at a [particular temperature is called an unsaturated solution.
Supersaturated Solution
The solution which contains even more amount of solute required to prepare saturated solution is called super saturated solution. The hot saturated solution of compound like sodium thiosulphate does not crystallize its solute if cooled slowly without disturbance. Such a solution is called supersaturated solution.
Dilute Solution
A solution which contains small amount of a solute as compared to the solvent is called dilute solution.
Concentrated Solution
A solution which contains excess amount of a solute as compared to that of a solvent is called a concentrated solution.
Concentrated Solution
The amount of solute present in given quantity of solvent is called concentration of solution. The concentration of a solution can be expressed in many ways depending upon the amount o solute and solvent present in it.
Concentration of Solution
The amount of solute present in given quantity of solvent is called concentration of solution. The concentration of a solution can be expressed in many ways depending upon the amount of solute and solvent present in it.
Percentage by Mass
The percentage of solute by mass is the mass of solute present in hundred part of the solution. For example 5% hydrogen peroxide solution by mass means that 5g hydrogen peroxide are dissolved in 95g of water to give 100g of solution.
Percentage of Mass = (Mass of Solute/Mass of Solution) x 100
Percentage by Volume
The concentration unit expresses the volume of solute present in 100cm3 of solution. For example 15% solution of alcohol by volume will mean that 15cm3 alcohols are present in 100cm3 of solution. (Here 3 represents cube)
Percentage by Volume = (Volume of Solute/Volume of Solution) x 100
Molar Solution
The solution that contains one mole of solute in 1dm3 of solution is called a molar solution. The concentration of this solution is expressed as M.
Molarity
Molarity of a solution is the number of moles of solute present in 1dm3 of the solution. It is expressed as M.
M = Number of Moles of Solute/Volume of Solution in dm3
or
M = (Mass of solute/Molecular Mass) x (1/ Volume of Solution in dm3)
Crystallization
The process in which crystal separates from saturated solution on cooling is called crystallization. It is a useful process because it can be used to purify the impure solid compounds. It can also be used to separate a mixture of solids.
Hydration
The ions surrounded by solvent molecules in solution are called solvated ions. If water is a solvent these ions are called hydrated ions.
Suspension
A suspension in such a mixture in which solute particles do not dissolved in solvent and if filtrated its particles do not pass through the pores of filter paper.
Colloidal Solution
In a colloidal solution the solute particles are slightly bigger than those present in a true solution but not big enough to seen with naked eye.
Standard Solution
A solution whose molarity (strength) is known is called Standard Solution.
True Solution
A True Solution is such a mixture in which solute particles are completely homogenized in the solvent for example solution of sodium chloride or copper sulphate in water.
Solubility
Solubility o a solute in a particular solvent is defined as the amount of solute in grams, which can dissolve in 100g of the solvent at a particular temperature to give a saturated solution.
or
The amount of a solute in gram moles, which can dissolve in one kilogram of the solvent at a particular temperature, to give a saturated solution.
Factors Affecting the Solubility
Effect of Solvent
Similar solvents dissolve similar solutes, i.e. if the chemical structure and the electrical properties such as dipole moment of solute and solvent are similar, the solubility will increase. If there is dissimilarity in properties, then either the solute will not dissolve or there will be very little solubility.
Effect of Solute
Different solutes have different solubility’s in a particular solvent e.g. if the saturated solutions of table sugar and sodium chloride are prepared, it is found that the concentration of sodium chloride solution is 5.3 molar while that of sugar solution is 3.8 molar. In other words, the solubility of sodium chloride in water is far greater than that of sugar. This is due to the fact that the attraction of sodium (Na+ and chloride (Cl-) ions with water is greater than that of sugar molecules with water.
Effect of Temperature
Change in temperature has different effects on the solubility of different compounds. Usually the solubility increase with the increase in temperature but it cannot be taken as a general rule. The solubility of compounds like lithium carbonate, calcium chromate decreases with the increase in temperature. The solubility of gases in water also decreases with the increase in temperature. On the other hand, there are a large number of compounds whose solubility in water increase with the increase in temperature e.g. sodium nitrate, silver nitrate, Potassium chloride etc. the solubility of sodium chloride in water does not increase appreciably with the increase in temperature.
A homogeneous mixture of different chemical substances which has uniform chemical composition through out and shows uniform physical properties is called solution. For example dissolve a small amount of copper sulphate in water the water will become blue. If this blue liquid is filtered, it will pass through the filter paper without leaving any solid. The mixture thus prepared is called a solution.
Binary Solution
A solution which is formed by mixing two substances is called binary solution. For example solution of glucose and water.
Solute
The component of a binary solution which is in lesser amount is called solute. For example in copper sulphate solution, copper sulphate is solute.
Solvent
The component of a binary solution which is in greater amount is called solvent. For example in copper sulphate solution, water is solvent.
Saturated solution
A solution in which maximum amount of a solute has been dissolved at a particular temperature and in which the dissolved form of solute is at equilibrium with its undissolved form is called saturated solution.
Unsaturated Solution
Solution which can dissolve further amount of a solute at a [particular temperature is called an unsaturated solution.
Supersaturated Solution
The solution which contains even more amount of solute required to prepare saturated solution is called super saturated solution. The hot saturated solution of compound like sodium thiosulphate does not crystallize its solute if cooled slowly without disturbance. Such a solution is called supersaturated solution.
Dilute Solution
A solution which contains small amount of a solute as compared to the solvent is called dilute solution.
Concentrated Solution
A solution which contains excess amount of a solute as compared to that of a solvent is called a concentrated solution.
Concentrated Solution
The amount of solute present in given quantity of solvent is called concentration of solution. The concentration of a solution can be expressed in many ways depending upon the amount o solute and solvent present in it.
Concentration of Solution
The amount of solute present in given quantity of solvent is called concentration of solution. The concentration of a solution can be expressed in many ways depending upon the amount of solute and solvent present in it.
Percentage by Mass
The percentage of solute by mass is the mass of solute present in hundred part of the solution. For example 5% hydrogen peroxide solution by mass means that 5g hydrogen peroxide are dissolved in 95g of water to give 100g of solution.
Percentage of Mass = (Mass of Solute/Mass of Solution) x 100
Percentage by Volume
The concentration unit expresses the volume of solute present in 100cm3 of solution. For example 15% solution of alcohol by volume will mean that 15cm3 alcohols are present in 100cm3 of solution. (Here 3 represents cube)
Percentage by Volume = (Volume of Solute/Volume of Solution) x 100
Molar Solution
The solution that contains one mole of solute in 1dm3 of solution is called a molar solution. The concentration of this solution is expressed as M.
Molarity
Molarity of a solution is the number of moles of solute present in 1dm3 of the solution. It is expressed as M.
M = Number of Moles of Solute/Volume of Solution in dm3
or
M = (Mass of solute/Molecular Mass) x (1/ Volume of Solution in dm3)
Crystallization
The process in which crystal separates from saturated solution on cooling is called crystallization. It is a useful process because it can be used to purify the impure solid compounds. It can also be used to separate a mixture of solids.
Hydration
The ions surrounded by solvent molecules in solution are called solvated ions. If water is a solvent these ions are called hydrated ions.
Suspension
A suspension in such a mixture in which solute particles do not dissolved in solvent and if filtrated its particles do not pass through the pores of filter paper.
Colloidal Solution
In a colloidal solution the solute particles are slightly bigger than those present in a true solution but not big enough to seen with naked eye.
Standard Solution
A solution whose molarity (strength) is known is called Standard Solution.
True Solution
A True Solution is such a mixture in which solute particles are completely homogenized in the solvent for example solution of sodium chloride or copper sulphate in water.
Solubility
Solubility o a solute in a particular solvent is defined as the amount of solute in grams, which can dissolve in 100g of the solvent at a particular temperature to give a saturated solution.
or
The amount of a solute in gram moles, which can dissolve in one kilogram of the solvent at a particular temperature, to give a saturated solution.
Factors Affecting the Solubility
Effect of Solvent
Similar solvents dissolve similar solutes, i.e. if the chemical structure and the electrical properties such as dipole moment of solute and solvent are similar, the solubility will increase. If there is dissimilarity in properties, then either the solute will not dissolve or there will be very little solubility.
Effect of Solute
Different solutes have different solubility’s in a particular solvent e.g. if the saturated solutions of table sugar and sodium chloride are prepared, it is found that the concentration of sodium chloride solution is 5.3 molar while that of sugar solution is 3.8 molar. In other words, the solubility of sodium chloride in water is far greater than that of sugar. This is due to the fact that the attraction of sodium (Na+ and chloride (Cl-) ions with water is greater than that of sugar molecules with water.
Effect of Temperature
Change in temperature has different effects on the solubility of different compounds. Usually the solubility increase with the increase in temperature but it cannot be taken as a general rule. The solubility of compounds like lithium carbonate, calcium chromate decreases with the increase in temperature. The solubility of gases in water also decreases with the increase in temperature. On the other hand, there are a large number of compounds whose solubility in water increase with the increase in temperature e.g. sodium nitrate, silver nitrate, Potassium chloride etc. the solubility of sodium chloride in water does not increase appreciably with the increase in temperature.
Class IX, CHEMISTRY, "States of Matter"
States of Matter
Matter has three states:
1. Gas
2. Liquid
3. solid
These are physical states of matter. The three states of one matter may have different physical properties while their chemical properties are same. Water exists in three physical states solid (ice), liquid and gas(steam) has same chemical properties.
Kinetic Theory of Matter
The Kinetic theory was presented to explain the properties of gases and is called kinetic theory of gases. But this theory was also able to explain the composition of liquid and solid state of matter. So its is called Kinetic Theory of Matter.
According to Kinetic Theory of matter:
1. All matter is composed of atoms, molecules or ions.
2. These particles have kinetic energy due to which they are in the state of motion.
3. In gaseous state, these particles move in a straight line. They collide with one another and with the walls of container. In liquids the rate of their movement is very small but in solids, there is to and fro motion only.
4. Generally material particles can have three types of movements, i.e. translational, rotational and vibrational.
Solids
The state of matter which has definite shape and volume is called solid.
Properties of Solids
1. Definite Volume and Shape
The cohesive forces in solid substances are so strong that they keep their particles arranged in fixed positions. So due to restrict movements of particles, the solids have definite volume and shape.
2.Motion of Particles
The solid particles have vibrational motion only because these particles are held in fixed position by strong cohesive forces.
3. Effect of Heat
The physical state of solid substance can be changed by heating. On heating solid is converted to liquid and gaseous state. Heat increases the kinetic energy of the particles and they start vibrating at higher frequency. At a particular temperature the vibrational motions become fast that they overcome the cohesive forces and solid melts to liquid.
4. Melting Point
The temperature at which the solid is converted to liquid on heating is called melting point. At melting point, the particles of solid loose their means position and their arrangement. The solid collapses and turns to liquid.
5. Sublimation
The conversion of some solids directly into gaseous state on heating is called sublimation. Iodine, ammonium chloride and naphthalene change directly into vapour state upon heating.
Liquid
The state of matter having definite volume but indefinite shape is called liquid.
Properties of Liquid
1. Volume
Liquids have definite volume. In liquid particles are very close to one another and have cohesive forces among the particles. Due to the presence of cohesive forces, liquids have definite volume and keep their level as well.
2. Shape
Liquids do not have any specific shape. They adopt the shape of the container. The molecules of liquid are able to move. Due to this random motion the molecules of liquid do not have fixed position and as a result, a liquid does not have any specific shape.
3. Evaporation
Conversion of liquid into its vapours at any temperature is called evaporation. The molecules of liquid come to the surface of liquid and escape by overcoming cohesive forces. So liquid is converted to vapours at all temperature.
4. Boiling Point
The temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure is called boiling point.
Gas
The state of matter which does not have definite shape and volume is called gaseous state.
Properties of Gaseous State
1. Indefinite Volume and Shape
In gaseous state, the molecules have insignificant cohesive forces among themselves. They move very fast in all possible directions. As a result, a gas neither has fixed shape nor a fixed volume.
2. Kinetic Energy of the Particle of a Gas
Gas particles have very high kinetic energy as compared to liquid and solid state.
3. Pressure
The molecules of a gas are in the state of random motion. The molecules of gas not only collide with one another but also with the walls of the container in which they are enclosed. Due to their collision, the velocity of the molecules changes every moment. The pressure exerted by gas is also due to the collision of its molecules with the walls of the container.
4. Elastic Collision
The collision of gas molecules is elastic in nature which means that the total energy of the colliding molecules remains the same before and after the collision.
5. Kinetic Energy
The kinetic energy of molecules of gas is very high as compared with solid and liquid.
Diffusion
The movement of molecules from a higher concentration to a lower concentration is known as Diffusion.
If the concentration of molecules at a particular place is higher, they start moving towards a place where their concentration is lower. When the concentration of molecules at both the places becomes equal the process of diffusion stops.
Diffusion in Gases
The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread uniformly throughout the room. The liquid perfume present in the bottle volatilized slowly and its vapours diffuse through out the room.
Graham’s Law of Diffusion
Scottish Chemist, Thomas Graham (1833) discovered that lighter gs can diffuse through porous pot faster than the heavier one. This is called Graham’s
Law of Diffusion.
Hydrogen being lighter gas will diffuse faster than oxygen or carbon dioxide.
Diffusion in Liquids
Liquid molecules can also diffuse because they have free movement. Since the molecules of liquid move comparatively slowly than gas molecule, their rate of diffusion are also lesser than gases.
Brownian Movement
Robert Brown (1927) discovered this phenomenon:
The free movement of the molecules of gases and liquid is called Brownian Movement.”
When a pollen grain is put in water. The movement of pollen grain in water is observed by microscope. It is observed that pollen grain is continuously moving in all directions. This free movement of pollen grain was due to the free movement of water molecules. The colliding water molecules will also force pollen grain to move as well. The students can observe Brownian movement with the help of simple experiment.
Experiment
Put a drop of milk on a microscope slide and cover it with cover slip. Put it under microscope and observe it. You will see small particle of fat moving randomly in milk. The movement of fat particles is actually due to the movement of water molecules in milk.
Matter has three states:
1. Gas
2. Liquid
3. solid
These are physical states of matter. The three states of one matter may have different physical properties while their chemical properties are same. Water exists in three physical states solid (ice), liquid and gas(steam) has same chemical properties.
Kinetic Theory of Matter
The Kinetic theory was presented to explain the properties of gases and is called kinetic theory of gases. But this theory was also able to explain the composition of liquid and solid state of matter. So its is called Kinetic Theory of Matter.
According to Kinetic Theory of matter:
1. All matter is composed of atoms, molecules or ions.
2. These particles have kinetic energy due to which they are in the state of motion.
3. In gaseous state, these particles move in a straight line. They collide with one another and with the walls of container. In liquids the rate of their movement is very small but in solids, there is to and fro motion only.
4. Generally material particles can have three types of movements, i.e. translational, rotational and vibrational.
Solids
The state of matter which has definite shape and volume is called solid.
Properties of Solids
1. Definite Volume and Shape
The cohesive forces in solid substances are so strong that they keep their particles arranged in fixed positions. So due to restrict movements of particles, the solids have definite volume and shape.
2.Motion of Particles
The solid particles have vibrational motion only because these particles are held in fixed position by strong cohesive forces.
3. Effect of Heat
The physical state of solid substance can be changed by heating. On heating solid is converted to liquid and gaseous state. Heat increases the kinetic energy of the particles and they start vibrating at higher frequency. At a particular temperature the vibrational motions become fast that they overcome the cohesive forces and solid melts to liquid.
4. Melting Point
The temperature at which the solid is converted to liquid on heating is called melting point. At melting point, the particles of solid loose their means position and their arrangement. The solid collapses and turns to liquid.
5. Sublimation
The conversion of some solids directly into gaseous state on heating is called sublimation. Iodine, ammonium chloride and naphthalene change directly into vapour state upon heating.
Liquid
The state of matter having definite volume but indefinite shape is called liquid.
Properties of Liquid
1. Volume
Liquids have definite volume. In liquid particles are very close to one another and have cohesive forces among the particles. Due to the presence of cohesive forces, liquids have definite volume and keep their level as well.
2. Shape
Liquids do not have any specific shape. They adopt the shape of the container. The molecules of liquid are able to move. Due to this random motion the molecules of liquid do not have fixed position and as a result, a liquid does not have any specific shape.
3. Evaporation
Conversion of liquid into its vapours at any temperature is called evaporation. The molecules of liquid come to the surface of liquid and escape by overcoming cohesive forces. So liquid is converted to vapours at all temperature.
4. Boiling Point
The temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure is called boiling point.
Gas
The state of matter which does not have definite shape and volume is called gaseous state.
Properties of Gaseous State
1. Indefinite Volume and Shape
In gaseous state, the molecules have insignificant cohesive forces among themselves. They move very fast in all possible directions. As a result, a gas neither has fixed shape nor a fixed volume.
2. Kinetic Energy of the Particle of a Gas
Gas particles have very high kinetic energy as compared to liquid and solid state.
3. Pressure
The molecules of a gas are in the state of random motion. The molecules of gas not only collide with one another but also with the walls of the container in which they are enclosed. Due to their collision, the velocity of the molecules changes every moment. The pressure exerted by gas is also due to the collision of its molecules with the walls of the container.
4. Elastic Collision
The collision of gas molecules is elastic in nature which means that the total energy of the colliding molecules remains the same before and after the collision.
5. Kinetic Energy
The kinetic energy of molecules of gas is very high as compared with solid and liquid.
Diffusion
The movement of molecules from a higher concentration to a lower concentration is known as Diffusion.
If the concentration of molecules at a particular place is higher, they start moving towards a place where their concentration is lower. When the concentration of molecules at both the places becomes equal the process of diffusion stops.
Diffusion in Gases
The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread uniformly throughout the room. The liquid perfume present in the bottle volatilized slowly and its vapours diffuse through out the room.
Graham’s Law of Diffusion
Scottish Chemist, Thomas Graham (1833) discovered that lighter gs can diffuse through porous pot faster than the heavier one. This is called Graham’s
Law of Diffusion.
Hydrogen being lighter gas will diffuse faster than oxygen or carbon dioxide.
Diffusion in Liquids
Liquid molecules can also diffuse because they have free movement. Since the molecules of liquid move comparatively slowly than gas molecule, their rate of diffusion are also lesser than gases.
Brownian Movement
Robert Brown (1927) discovered this phenomenon:
The free movement of the molecules of gases and liquid is called Brownian Movement.”
When a pollen grain is put in water. The movement of pollen grain in water is observed by microscope. It is observed that pollen grain is continuously moving in all directions. This free movement of pollen grain was due to the free movement of water molecules. The colliding water molecules will also force pollen grain to move as well. The students can observe Brownian movement with the help of simple experiment.
Experiment
Put a drop of milk on a microscope slide and cover it with cover slip. Put it under microscope and observe it. You will see small particle of fat moving randomly in milk. The movement of fat particles is actually due to the movement of water molecules in milk.
Class IX, CHEMISTRY, "Periodicity of Elements and Periodic Table"
Periodicity of Elements and
Periodic Table
Definitions
Periodic Table
A table of elements obtained by arranging them in order of their increasing atomic number in which elements having similar properties are placed in the same group is called Periodic Table.
Group
The vertical column of elements in the periodic table are called Groups.
Period
The horizontal rows of elements in the periodic table are called Periods.
Periodicity
The repetition of physical and chemical properties of elements periodically is called Periodicity of Properties.
Periodic Law
Physical and chemical properties of elements are periodic function of their atomic masses.
Metal
Elements which are good conductors of heat and electricity are malleable and ductile and have a metallic luster are called Metals like Sodium, Potassium, Gold, Copper etc.
Non-Metals
Elements which are non or bad conductor of heat and electricity are neither malleable or ductile and have no metallic luster are called Non-Metals like Carbon, Nitrogen, Chlorine etc.
Metalloids
Metalloids are semi metals have the properties which are intermediate between a metal and non-metal like Boron, Silicon, Germanium, Arsenic, Antimony etc.
Law of Triads
A German Chemist, Dobereiner (1829), arranged chemically similar elements in groups of three on the basis of their atomic masses called Triads and it was found that atomic mass of the middle element was approximately equal to the average of atomic masses of other two elements. This is known as Law of Triads.
Drawback or Defect
As very few elements could be arranged in such groups, this classification did not get wide acceptance.
Law of Octaves
An English Chemist Newland (1864) stated that if the elements were arranged in the ascending order of their atomic masses, every eight element will have similar properties to the first. This is knows as Law of Octaves.
Drawback or Defects
1. Noble gases were not discovered at that time and no place was reserved for the undiscovered noble gases.
2. In the same way no blank spaces for the undiscovered elements were present in his table.
Mendeleyv’s Period Table and Periodic Law
Russian Chemist, Mendeleyv’s (186) who wa working separately from Lother Mayer published a table of elements.
According to Mendeleyv’s when the element were arranged in order of their increasing atomic mases, the elements with similar properties were repeated after regular interval and were placed one above the other. A table obtained in this manner is called Periodic Table. Mendeleyv’s stated this periodicity in the form of Periodic Law.
Important Features of Mendeleyv’s Periodic Table
The important features of Mendeleyv’s Periodic table are:
Periods and Groups
The horizontal rows which run from left to right in Periodic Table are called Periods and they are twelve in number.
The vertical rows which run from top to bottom in periodic table are called groups and they are eight in number.
Vacant Spaces
Mendeleyv’s left many vacant spaces for the still unknown elements. For example, next to Calcium (40) should be Titanium (48) but it resembled silicon (28) instead of Aluminium (27). He left vacant space for element with atomic mass 44.
Discovery of New Element
Mendeleyv’s discovered new elements and also guessed their atomic mass and properties.
Atomic Mass Correction
Mendeleyv’s corrected the atomic masses of certain elements on basis of their properties and provided proper place to them in the periodic table.
Defects in Mendeleyv’s Periodic Table
The Mendeleyv’s Period Table has following defects:
Irregular Position of Some Elements
According to Mendeleyv’s Periodic Law Potassium (39) should be placed before Argon (40) but he placed Argon (40) before Potassium (39) which goes against his law.
Position of Isotopes
Mendeleyv’s periodic table gives no indication about the position of isotopes.
Structure of Atom
Mendeleyv’s Periodic table gives no idea about structure of atoms.
Position of Lanthanides and Actinides
Lanthanides and Actinides have not been given proper place in Periodic Table.
Coinage and Alkali Metals
Alkali metals and coinage metals with different properties are placed in the same group. This defect has been replaced by placing them into two sub groups.
Modern Periodic Law and Modern Periodic Table
Modern Periodic Law
Physical and chemical properties of the elements are periodic function of their atomic number. Mosely (1913) says that atomic mas is not fundamental property. Due to some defects present in Mendeleyv’s periodic law, Mosely introduced the concept of anomic number for the elements.
Example
When isotopes were discovered, it was thought advisable to arrange the elements on basis of their atomic number instead o increasing atomic mases. Isotopes were needed different position in the Mendeleyv’s periodic table. Hence Mendeleyv’s periodic law was modified.
Modern Periodic Table
When Mendeleyv’s periodic law was modified and new elements were discovered. This forcd the scientists to change Mendeleyv’s periodic law.
The electronic configuration of atoms also played an important role in he arrangement of the modern periodic law. This form of periodic table is called “Long form of Periodic Table” because it contains eighteen groups instead of eight but seven periods instead of twelve.
Group I – The Alkali Metals
The elements of group I are called “Alkali Metals”. The word alkali is derived from an Arabic word meaning Ashes.
Elements of Group I
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium
Properties of Group I
1. They are mono atomic.
2. They exist in solid metallic state.
3. Outer most shell of these elements is incomplete having one electron.
4. Elements of this group are highly reactive.
5. Elements of this group have large tendency to form compounds.
6. Elements of this group are strongly electro-positive.
Group II – The Alkaline Earth Metals
The elements of group II are called Alkaline Earth Metals. These elements occur in nature as silicate mineral and their oxides and hydroxides are strongly basic. Therefore these elements are called Alkaline Earth Metals.
Elements of Group II
Beryllium
Magnesium
Calcium
Strontium
Barium
Radium
Properties of Group II
1. They are mono atomic.
2. They exist in solid state.
3. Outer most shell of these elements is incomplete having two electrons.
4. Elements of this group are moderately reactive.
5. Elements of this group have moderate tendency to form compounds.
Group III – The Boron or Aluminium Family
The elements of group III exist in solid state.
Elements of Group III
Boron Metalloid
Aluminium Metal
Gallium Metal
Indium Metal
Thallium Metal
Properties of Group III
1. They are mono atomic.
2. They exist in solid state.
3. Outer most shell of these elements is incomplete having three electrons.
4. Elements of this group are quite reactive.
5. Elements of this group have moderate tendency to form compounds.
Group IV – The Carbon and Silicon Family
Elements of Group IV
Carbon
Silicon
Germanium
Tin
Lead
Properties of Group IV
1. They are mono atomic.
2. They exist in solid state.
3. Outermost shell of these elements is incomplete.
4. Elements of this group are quite reactive.
5. Elements of this group have moderate tendency to form compounds.
Group V – The Nitrogen Family
Elements of Group V
Nitrogen
Phosphorus
Arsenic
Antimony
Bismuth
Properties of Group V
1. Some are mono atomic and some are di-atomic.
2. Some of them exist in gaseous and some are in solid state.
3. Outermost shell of these elements is incomplete having five electrons.
4. elements of this group are quite reactive.
5. Elements of this group have quite tendency to form compound.
Group VI – The Oxygen Family
Elements of Group VI
Oxygen
Sulphur
Selenium
Tellurium
Polonium
Properties of Group VI
1. Some are mono atomic and some are di-atomic.
2. Some of them exist in gaseous and some are in solid state.
3. Elements of this group have quite tendency to form compounds.
4. The tendency of forming covalent bond decreases from oxygen to polonium.
5. There is a gradual decrease in the ionization potential down the group.
Group VII – The Halogen Family
Elements of Group VII
Fluorine Gas
Chlorine Gas
Bromine Liquid
Iodine Solid
Astatine Radioactive
Properties of Group VII
1. They are diatomic except At.
2. Halogens are very active non-metals.
3. Outer most shell of these elements is incomplete having seven electrons.
4. Elements of this group are highly reactive.
5. There is a gradual decrease in the ionization potential down the group.
Transition Elements
Definition
Elements in Group IB, IIB, through VIIB are known as Transition Elements because they show their properties which are transitional between higly reactive and strong electro-positive elements of S-block which form ionic compounds and p-block elements which form largely covalent compounds.
Properties of Transition Elements
1. Transition Elements have incomplete inner electron shells.
2. They show variable valency.
3. They show similar behaviour.
4. They all are metals.
5. They have strong inner atomic bonds.
Group 0, The Noble Gases
The elements of Group VIII A are called “Noble Gases” or “Inert Gases” or “Zero Group Elements”.
Elements of Group 0
Helium
Neon
Argon
Krypton
Xenon
Radon
Properties of Group 0
1. They are mono atomic.
2. They exist in gaseous state.
3. Outer most shell of these elements is either complete or contains eight electrons.
4. These elements are mostly chemically non-reactive.
5. These elements have no tendency to form compounds (only a few of these compounds are known).
Atomic Radius
Definition
One half of the distance between the nucleus of two identical atoms when these are in close contact with each other is called Atomic Radius.
Unit
It is measured in angstrom unit A.
Trend in Period
The atomic radii decreases from left to right within a period in the periodic table. This is because nuclear charge increases with the increase of atomic number. But the number of shells remains same within a period.
Trend in Group
Atomic radius increases from top to bottom in a group. This is because, although nuclear charge increases from top to bottom but at the same time on new shell is also added for each successive element down the group.
Ionization Energy (I.E) or Ionization Potential (I.P)
Definition
The minimum energy needed to remove an electron from an isolated, gaseous atom in its ground state is called Ionization Energy.
Unit
It is expressed in electron volts or kilo-joules permole.
1 ev = 96.49kj
Factors Affecting Ionization Energy
The ionization energy of elements depends upon the following factors:
1. Effect of Nuclear Charge on I.E
The greater the nuclear charge the higher is the ionization energy.
2. Effect of Atomic Size
The larger the size of atom the lower is the ionization energy.
Trend of I.E in Period
Ionization energy increases from left to right in a period due to increase in nuclear change and decrease in atomic size.
Trend of I.E in Group
I.E decreases from top to bottom in a group due to increase in atomic size.
Electronegativity
Definition
The tendency of each atom in a covalent molecule to attract a shared pair of electrons towards itself is known as its electronegativity.
Factors Affecting Electronegativity
Electronegativity depends upon the following factors:
Atomic size
Atomic Number
Electron Affinity
Ionization Energy
Trend or Variation in the Period
Electronegativity increases from left to right within a period due to increase in nuclear charge and decrease in atomic size.
Trend or Variation in the Group
Electronegativity values decreases from top to bottom within a group due to increase in atomic size.
Electron Affinity
Definition
The energy change that occurs when an electron is gained by an atom in the gaseous state is known as Electron Affinity.
Electron Affinity for the addition of first electron is negative i.e. energy is released but for further addition of electrons it is positive because energy has to be added to over come repulsion between negative ion and electron.
Unit
It is measured in KJ/mol or in e.v per atom.
Factors Affecting Electron Affinity
Atomic Size
Nuclear Charge
Trend or Variation of Electron Affinity in Group
Down the group in the periodic table, electron affinity decreases because the addition of a new shell to each atom decreases its force of attraction.
Trend or Variation of Electron Affinity in Period
In a period, the electron affinity increases from left to right because the incoming successive atoms have higher nuclear charge and attract electron more towards itself.
Class IX, CHEMISTRY, "Atomic Structure"
Dalton’s Atomic Theory
The important postulates of Dalton’s atomic theory are:
1. All elements are composed of atoms. Atom is too small so that it could not be divided into further simpler components.
2. Atom cannot be created nor destroyed in any chemical reactions.
3. Atoms of an element are similar in all respects. They have same mass and properties.
4. Atoms of different elements combine in a definite simple ratio to produce compounds.
Discovery of Electron
A discharge tube is a glass tube. It has two electrode, a source of electric current and a vacuum pump.
(Diagram)
Sir William Crooks (1895 performed experiments by passing electric current through gas in the discharge tube at very low pressure. He observed that at 10-4 (-4 is power to 10) atmosphere pressure, shining rays are emitted from cathode. These rays were named cathode rays. Cathode rays are material particles as they have mass and momentum.
Properties of Cathode Rays
The properties of these particles are given below:
1. These particles are emitted from cathode surface and move in straight line.
2. The temperature of the object rises on which they fall.
3. They produce shadow of opaque object placed in their path.
4. These particles are deflected in electric and magnetic fields.
5. These particles are deflected towards positive plate of electric field.
Discovery of Proton
Gold Stein (1886) observed that in addition to the cathode rays, another type of rays were present in the discharge tube. These rays travel in a direction opposite to cathode rays. These rays were named positive rays. By using perforated cathode in the discharge tube the properties of these rays can be studied. Positive rays are also composed of metered particles. The positive rays are not emitted from anode. They are produced by the ionization of residual gas molecules in the discharge tube. When cathode rays strike with gas molecule, electrons are removed and positive particles are produced.
Properties of Positive Rays
1. They are deflected towards negative plate of electric field. Therefore these rays carry positive charge.
2. The mass of positive rays is equal to the mass of the gas enclosed in the discharge tube.
3. The minimum mass of positive particles is equal to the mass of hydrogen ion (H+). These positive ions are called Protons.
4. The charge on proton is equal to +1.602×10-19 Coulomb. (-19 is power of 10)
Natural Radioactivity
The phenomenon in which certain elements emit radiation which can cause fogging of photographic plate is called natural radioactivity. The elements which omit these rays are called radioactive elements like Uranium, Thorium, Radium etc. There are about 40 radioactive elements. Henri Bequrel (1896) discovered radioactivity.Madam Curei also has valuable contribution in this field.
In natural radioactivity nuclei of elements are broken and element converted to other elements. Natural radioactivity is nuclear property of the elements.
Alpha Rays
1. They are helium nuclei. They are doubly positively charged, He2+.
2. They move with speed equal to the 1/10th of the velocity of the light.
3. They cannot pass through thick-metal foil.
4. They are very good ionizer of a gas.
5. They affect the photographic plate.
Beta Rays
1. They are negatively charged.
2. They move with the speed equal to the velocity of light.
3. They can pass through a few millimeter thick metal sheets.
4. They are good ionizer of a gas.
5. They can affect the photographic plate.
Gamma Rays
1. They are electromagnetic radiations.
2. They travel with speed equal to velocity of light.
3. They carry no charge.
4. They have high penetration power than alpha and beta rays.
5. They are weak ionizer of gas.
Rutherford Experiment and Discovery of Nucleus
Lord Rutherford (1911) and his coworkers performed an experiment. They bombarded a very thin, gold fail with Alpha particles from a radioactive source. They observed that most of the particles passed straight through the foil undeflected. But a few particles were deflected at different angles. One out of 4000 Alpha particles was deflected at an angle greater than 150.
(Diagram)
Conclusion
Following conclusions were drawn from the Rutherford’s Alpha Particles scattering experiment.
1. The fact that majority of the particles went through the foil undeflected shows that most of the space occupied by an atom is empty.
2. The deflection of a few particles over a wide angle of 150 degrees shows that these particles strike with heavy body having positive charge.
3. The heavy positively charged central part of the atom is called nucleus.
4. Nearly all of the mass of atom is concentrated in the nucleus.
5. The size of the nucleus is very small as compared with the size of atom.
Defects of Rutherford Model
Rutherford model of an atom resembles our solar system. It has following defects:
1. According to classical electromagnetic theory, electron being charged body will emit energy continuously. Thus the orbit of the revolving electron becomes smaller and smaller until it would fall into the nucleus and atomic structure would collapse.
2. If revolving electron emits energy continuously then there should be a continuous spectrum but a line spectrum is obtained.
(Diagram)
Bohr’s Atomic Model
Neil Bohr (1913) presented a model of atom which has removed the defects of Rutherford Model. This model was developed for hydrogen atom which has only proton in the nucleus and one electron is revolving around it.
Postulates of Bohr’s Atomic Model
The main postulates of Bohr’s Model are given below:
1. Electrons revolve around the nucleus in a fixed orbit.
2. As long as electron revolves in a fixed orbit it does not emit and absorb energy. Hence energy of electron remains constant.
3. The orbit nearest to the nucleus is the first orbit and has lowest energy. When an electron absorbs energy it jumps from lower energy orbit to higher energy orbit. Energy is emitted in the form of radiations, when an electron jumps from higher energy orbit to lower energy orbit. The unit of energy emitted in the form of radiations is called quantum. It explains the formation of atomic spectrum.
4. The change in energy is related with the quantum of radiation by the equation :
E2 – E1 = hv
where
E1 = Energy of first orbit
E2 = Energy of the second orbit
h = Planck’s constant
v = Frequency of radiation
Atomic Number
The number of protons present in the nucleus of an atom is called atomic number or proton number. It is denoted by z. The proton in the nucleus of an atom is equal to number of electrons revolving around its nucleus.
Mass Number
The total number of the protons and neutrons present in the nucleus of an atom is called mass number. The protons and neutrons together are called nucleon. Hence it is also known as nucleon number. It is denoted by A. the number of neutrons present in the nucleus of an atom is rperesented by N.
Mass Number = No of Protons + No of neutrons
A = Z + N
Isotopes
The atoms of same elements which have same atomic number but different mas number are called Isotopes. The number of protons present in the nucleus of an atom remains the same but number of neutrons may differ.
Isotopes of Different Elements
Isotopes of Hydrogen
Hydrogen has three isotopes:
1. Ordinary Hydrogen or Protium, H.
2. Heavy Hydrogen or Deutrium, D.
3. Radioactive Hydrogen or Tritium, T.
Protium
Ordinary naturally occurring hydrogen contains the largest percentage of protium. It is denoted by symbol H. It has one proton in its nucleus and one electron revolve around the nucleus.
Number of Protons = 1
Number of Electrons = 1
Number of Neutrons = 0
Atomic Number = 1
Mass Number = 1
Deutrium
Deutrium is called heavy hydrogen. The percentage of deutrium in naturally occuring hydrogen is about 0.0015%. It has one proton and one neutron in its nucleus. It has one electron revolving around its nucleus. It is denoted by symbol D.
Number of Proton = 1
Number of Electron = 1
Number of Neutrons = 1
Atomic Number = 1
Mass Number = 2
Tritium
Radioactive hydrogen is called tritium. It is denoted by symbol T. The number of tritium isotope is one in ten millions. It has one proton and 2 neutrons in its nucleus. It has one electron revolving around its nucleus.
Number of Proton = 1
Number of Electron = 1
Number of Neutron = 2
Atomic Number = 1
Mass Number = 3
The important postulates of Dalton’s atomic theory are:
1. All elements are composed of atoms. Atom is too small so that it could not be divided into further simpler components.
2. Atom cannot be created nor destroyed in any chemical reactions.
3. Atoms of an element are similar in all respects. They have same mass and properties.
4. Atoms of different elements combine in a definite simple ratio to produce compounds.
Discovery of Electron
A discharge tube is a glass tube. It has two electrode, a source of electric current and a vacuum pump.
(Diagram)
Sir William Crooks (1895 performed experiments by passing electric current through gas in the discharge tube at very low pressure. He observed that at 10-4 (-4 is power to 10) atmosphere pressure, shining rays are emitted from cathode. These rays were named cathode rays. Cathode rays are material particles as they have mass and momentum.
Properties of Cathode Rays
The properties of these particles are given below:
1. These particles are emitted from cathode surface and move in straight line.
2. The temperature of the object rises on which they fall.
3. They produce shadow of opaque object placed in their path.
4. These particles are deflected in electric and magnetic fields.
5. These particles are deflected towards positive plate of electric field.
Discovery of Proton
Gold Stein (1886) observed that in addition to the cathode rays, another type of rays were present in the discharge tube. These rays travel in a direction opposite to cathode rays. These rays were named positive rays. By using perforated cathode in the discharge tube the properties of these rays can be studied. Positive rays are also composed of metered particles. The positive rays are not emitted from anode. They are produced by the ionization of residual gas molecules in the discharge tube. When cathode rays strike with gas molecule, electrons are removed and positive particles are produced.
Properties of Positive Rays
1. They are deflected towards negative plate of electric field. Therefore these rays carry positive charge.
2. The mass of positive rays is equal to the mass of the gas enclosed in the discharge tube.
3. The minimum mass of positive particles is equal to the mass of hydrogen ion (H+). These positive ions are called Protons.
4. The charge on proton is equal to +1.602×10-19 Coulomb. (-19 is power of 10)
Natural Radioactivity
The phenomenon in which certain elements emit radiation which can cause fogging of photographic plate is called natural radioactivity. The elements which omit these rays are called radioactive elements like Uranium, Thorium, Radium etc. There are about 40 radioactive elements. Henri Bequrel (1896) discovered radioactivity.Madam Curei also has valuable contribution in this field.
In natural radioactivity nuclei of elements are broken and element converted to other elements. Natural radioactivity is nuclear property of the elements.
Alpha Rays
1. They are helium nuclei. They are doubly positively charged, He2+.
2. They move with speed equal to the 1/10th of the velocity of the light.
3. They cannot pass through thick-metal foil.
4. They are very good ionizer of a gas.
5. They affect the photographic plate.
Beta Rays
1. They are negatively charged.
2. They move with the speed equal to the velocity of light.
3. They can pass through a few millimeter thick metal sheets.
4. They are good ionizer of a gas.
5. They can affect the photographic plate.
Gamma Rays
1. They are electromagnetic radiations.
2. They travel with speed equal to velocity of light.
3. They carry no charge.
4. They have high penetration power than alpha and beta rays.
5. They are weak ionizer of gas.
Rutherford Experiment and Discovery of Nucleus
Lord Rutherford (1911) and his coworkers performed an experiment. They bombarded a very thin, gold fail with Alpha particles from a radioactive source. They observed that most of the particles passed straight through the foil undeflected. But a few particles were deflected at different angles. One out of 4000 Alpha particles was deflected at an angle greater than 150.
(Diagram)
Conclusion
Following conclusions were drawn from the Rutherford’s Alpha Particles scattering experiment.
1. The fact that majority of the particles went through the foil undeflected shows that most of the space occupied by an atom is empty.
2. The deflection of a few particles over a wide angle of 150 degrees shows that these particles strike with heavy body having positive charge.
3. The heavy positively charged central part of the atom is called nucleus.
4. Nearly all of the mass of atom is concentrated in the nucleus.
5. The size of the nucleus is very small as compared with the size of atom.
Defects of Rutherford Model
Rutherford model of an atom resembles our solar system. It has following defects:
1. According to classical electromagnetic theory, electron being charged body will emit energy continuously. Thus the orbit of the revolving electron becomes smaller and smaller until it would fall into the nucleus and atomic structure would collapse.
2. If revolving electron emits energy continuously then there should be a continuous spectrum but a line spectrum is obtained.
(Diagram)
Bohr’s Atomic Model
Neil Bohr (1913) presented a model of atom which has removed the defects of Rutherford Model. This model was developed for hydrogen atom which has only proton in the nucleus and one electron is revolving around it.
Postulates of Bohr’s Atomic Model
The main postulates of Bohr’s Model are given below:
1. Electrons revolve around the nucleus in a fixed orbit.
2. As long as electron revolves in a fixed orbit it does not emit and absorb energy. Hence energy of electron remains constant.
3. The orbit nearest to the nucleus is the first orbit and has lowest energy. When an electron absorbs energy it jumps from lower energy orbit to higher energy orbit. Energy is emitted in the form of radiations, when an electron jumps from higher energy orbit to lower energy orbit. The unit of energy emitted in the form of radiations is called quantum. It explains the formation of atomic spectrum.
4. The change in energy is related with the quantum of radiation by the equation :
E2 – E1 = hv
where
E1 = Energy of first orbit
E2 = Energy of the second orbit
h = Planck’s constant
v = Frequency of radiation
Atomic Number
The number of protons present in the nucleus of an atom is called atomic number or proton number. It is denoted by z. The proton in the nucleus of an atom is equal to number of electrons revolving around its nucleus.
Mass Number
The total number of the protons and neutrons present in the nucleus of an atom is called mass number. The protons and neutrons together are called nucleon. Hence it is also known as nucleon number. It is denoted by A. the number of neutrons present in the nucleus of an atom is rperesented by N.
Mass Number = No of Protons + No of neutrons
A = Z + N
Isotopes
The atoms of same elements which have same atomic number but different mas number are called Isotopes. The number of protons present in the nucleus of an atom remains the same but number of neutrons may differ.
Isotopes of Different Elements
Isotopes of Hydrogen
Hydrogen has three isotopes:
1. Ordinary Hydrogen or Protium, H.
2. Heavy Hydrogen or Deutrium, D.
3. Radioactive Hydrogen or Tritium, T.
Protium
Ordinary naturally occurring hydrogen contains the largest percentage of protium. It is denoted by symbol H. It has one proton in its nucleus and one electron revolve around the nucleus.
Number of Protons = 1
Number of Electrons = 1
Number of Neutrons = 0
Atomic Number = 1
Mass Number = 1
Deutrium
Deutrium is called heavy hydrogen. The percentage of deutrium in naturally occuring hydrogen is about 0.0015%. It has one proton and one neutron in its nucleus. It has one electron revolving around its nucleus. It is denoted by symbol D.
Number of Proton = 1
Number of Electron = 1
Number of Neutrons = 1
Atomic Number = 1
Mass Number = 2
Tritium
Radioactive hydrogen is called tritium. It is denoted by symbol T. The number of tritium isotope is one in ten millions. It has one proton and 2 neutrons in its nucleus. It has one electron revolving around its nucleus.
Number of Proton = 1
Number of Electron = 1
Number of Neutron = 2
Atomic Number = 1
Mass Number = 3
Class IX, CHEMISTRY, "Chemical Combinations and Chemical Equations"
CHEMICAL COMBINATIONS
&
CHEMICAL REACTION
&
CHEMICAL REACTION
Laws of Chemical Combinations
There are four laws of chemical combinations these laws explained the general feature of chemical change. These laws are:
1. Law of Conservation of Mass
2. Law of Definite Proportions
3. Law of Multiple Proportions
4. Law Reciprocal Proportions
Antoine Lavoiser has rejected the worn out ideas about the changes that take place during a chemical reaction. He made careful quantitative measurements in chemical reactions and established that mass is neither created nor destroyed in a chemical change.
1. Law of Conservation of Mass
Statement
It is presented by Lavoiser. It is defined as:
“Mass is neither created nor destroyed during a chemical reaction but it only changes from one form to another form.”
In a chemical reaction, reactants are converted to products. But the total mass of the reactants and products remains the same. The following experiment easily proves law of conservation of mass.
Practical Verification (Landolt Experiment)
German chemist H. Landolt, studied about fifteen different chemical reactions with a great skill, to test the validity of the law of conservation of mass. For this, he took H-shaped tube and filled the two limbs A and B, with silver nitrate (AgNO3) in limb A and Hydrochloric Acid (HCl) in limb B. The tube was sealed so that material could not escape outside. The tube was weighed initially in a vertical position so that the solution should not intermix with each other. The reactant were mixed by inverting and shaking the tube. The tube was weighed after mixing (on the formation of white precipitate of AgCl). He observed that weight remains same.
HCl + AgNO3 ———> AgCl +
NaNO3
2. Law of Definite Proportions
Statement
It is presented by Proust. It is defined as:
“When different elements combine to give a pure compound, the ratio between the masses of these elements will always remain the same.”
Proust proved experimentally that compound obtained from difference source will always contain same elements combined together in fixed proportions.
Example
Water can be obtained from different sources such as river, ocean, well, canal, tube well, rain or by the chemical combination of hydrogen and oxygen. If different samples of water are analyzed, it will have two elements, hydrogen and oxygen and the ratio between their mass is 1:8.
3. Law of Multiple Proportions
Statement
This law is defined as:
“When two elements combine to give more than one compounds, the different masses of one element, which will combine with the fixed mass of other element, will be in simple whole number ratio.”
Two different elements can combine to form more than one compound. They can do so by combining in different ratios to give different compounds.
Example
Hydrogen and oxygen combine with one another to form water (H2O) and hydrogen peroxide (H2O2). In water and hydrogen oxide 2 g of hydrogen combine with 16g and 32g of oxygen respectively. According to law of multiple proportions, the different masses of oxygen (16g and 32g) which have reacted with fixed mass (2g) of hydrogen will have a simple ratio between each other i.e. 16:32 or 1:2. It means that hydrogen peroxide contains double the number of oxygen atoms than water. This law proves this point of Dalton’s Atomic Theory that atoms do not break in a chemical reaction.
4. Law of Reciprocal Proportions
Statement
This law is defined as:
“When two element A, B combine separately, with the mixed mass of the third element E, the ratio in which these elements combine with E is either the same or simple multiple of the ratio in which A and B combine with each other.”
Example
Hydrogen and Nitrogen separately combine to form ammonia (NH3) and dinitrogen oxide (N2O), in these compounds, fixed mass of nitrogen is 14g and combines with 8 g of oxygen and 3 g of hydrogen. The ratio between the mass of oxygen and hydrogen is 8:3. Hydrogen and oxygen also combine with one another to form water (H2O). The ratio between hydrogen and oxygen in water is 16:2. These ratios are not same. Let us observe whether these ratios are simple multiple to each other or not following mathematical operation is carried out.
8:3 ::16:2
8/3 : 16/2
or
8/3 x 2/16
or
1/3 => 1:3
Atom
It is the smallest particle of an element which can exist with all the properties of its own element but it cannot exist in atmosphere alone.
OR
The smallest particle of an element which cannot exist independently and
take part in a chemical reaction is known as Atom.Examples
Hexogen(H), Carbon (C), Sodium (Na), Gold (Au) etc.
Molecule
When two or more than two atoms are combined with each other a molecule is formed. It can exist freely in nature.
OR
The particle of a substance (Element or Compound) which can exist independently and show all the properties of that substance is called molecule.
Atoms of the same or different elements react with each other and form molecule.
Atoms of some elements can exist independently, since they have property of molecule so they are called mono atomic molecule.
Examples
Examples of Molecules of the elements are Hydrogen (H2). Nitrogen (N2), Oxygen (O2) etc.
Molecules of different elements are called compounds. For example HCl, H2O, CH4 etc.
Valency
The combining capacity of all elements with other elements is called valency.
Example
H = 1
C = 4
Al = 3
Mg = 2
Na = 1
Chemical Formula
“A brief name used for full chemical name at a compound is called Chemical Formula.”
A chemical formula is used to represent an element or a compound in terms of symbols. It also represents the number and type of atoms of elements present in the smallest unit of that substance.
Example
The chemical formula of hydrogen sulphide is H2S. It shows two types of elements (H and S) and number of
atoms of element (2H and 1S). Similarly the formula of NaCl show number and type of different atoms present in its smallest unit.
Formula Weight
It is the sum of the weights of the atoms present in the formula of a substance.
Molecular Weight
It is the sum of the atomic masses of all the atoms present in a molecule.
Empirical Formula
Definition It is the simplest formula of a chemical compound which represents the element present of the compound and also represent the simplest ratio between the elements of the compound.
Examples
·
The empirical formula of benzene is “CH”. It
indicates that the benzene molecule is composed of two elements carbon and
hydrogen and the ratio between these two elements is 1:1.
·
The empirical formula of glucose is “CH2O”.
This formula represents that glucose molecule is composed of three elements
carbon, hydrogen and oxygen. The ratio between carbon and oxygen is equal but
hydrogen is double.
Determination of Empirical Formula
To determine the empirical formula of a compound following steps are required.
1. To detect the elements present in the compound.
2. To determine the masses of each element.
3. To calculate the percentage of each element.
4. Determination of mole composition of each element.
5. Determination of simplest ratio between the element of the compound.
Illustrated Example of Empirical Formula
Consider an unknown compound whose empirical formula is to be determined is given to us. Now we will use the above five steps in order to calculate the empirical formula.
Step I – Determination of the Elements
By performing test it is found that the compound contains magnesium and oxygen elements.
Step II – Determination of the Masses
Masses of the elements are experimentally determined which are given below.
·
Mass of Mg = 2.4 gm
·
Mass of Oxygen = 1.6 gm
Step III – Estimation of the Percentage
The percentage of an element may be determined by using the formula.
% of element = Mass of element / Mass of compound x 100
In the given compound two elements are present which are magnesium and oxygen, therefore mass of compound is equal to the sum of the mass of magnesium and mass of oxygen.
Mass of compound = 2.4 + 1.6 = 4.0 gm
% of Mg = Mass of Mg / Mass of Compound x 100
= 2.4 / 4.0 x 100
= 60%
% of O = Mass of Oxygen / Mass of Compound x 100
= 1.6 / 4.0 x 100
= 40%
Step IV – Determination of Mole Composition
Mole composition of the elements is obtained by dividing percentage of each element with its atomic mass.
Mole ratio of Mg = Percentage of Mg / Atomic Mass of Mg
Mole ratio of Mg = 60 / 24
= 2.5
Mole ratio of O = Percentage of Oxygen / Atomic Mass of Oxygen
= 40 / 16
= 2.5
Step V – Determination of Simplest Ratio
To obtain the simplest ratio of the atoms the quotients obtained in the step IV are divided by the smallest quotients.
Simple ratio of Element = Value of Mole ratio / minimum Value of mole ratio
Simple ratio of Mg = 2.5 / 2.5
= 1
Simple ratio of O = 2.5 / 2.5
= 1
Thus the empirical formula of the compound is MgO
Note
If the number obtained in the simplest ratio is not a whole number then multiply this number with a smallest number such that it becomes a whole number maintain their proportion.
Molecular Formula
Definition
The formula which shows the actual number of atoms of each element present in a molecule is called molecular formula.
OR
It is a formula which represents the element ratio between the
elements and actual number of atoms of each type of elements present per molecule
of the compound.Examples
The molecular formula of benzene is “C6H6″. It indicates that
1. Benzene molecule is composed of two elements carbon and hydrogen.
2. The ratio between carbon and hydrogen is 1:1.
3. The number of atoms present per molecule of benzene are 6 carbon and 6 hydrogen atoms.
The molecular formula of glucose is “C6H12O6″. The formula represents that
1. Glucose molecule is composed of three elements carbon, hydrogen and oxygen.
2. The ratio between the atoms of carbon, hydrogen and oxygen is 1:2:1.
3. The number of atoms present per molecule of glucose are 6 carbon atoms. 12 hydrogen atoms and 6 oxygen atoms.
Determination of Molecular Formula
The molecular formula of a compound is an integral multiple of its empirical formula.
Molecular formula = (Empirical formula) n
Where n is a digit = 1, 2, 3 etc.
Hence the first step in the determination of molecular formula is to calculate its empirical formula by using the procedure as explained in empirical formula. After that the next step is to calculate the value of n
value of n = Molecular Mass / Empirical Formula Mass
Example
The empirical formula of a compound is CH2O and its molecular mass is 180.
To calculate the molecular formula of the compound first of all we will calculate its empirical formula mass.
Empirical formula mass of CH2O = 12 + 1 x 2 + 16
= 30
Value of n = Molecular Mass / Empirical Formula Mass
= 180 / 30
= 6
Molecular formula = (Empirical formula) n
= (CH2O) 6
= C6H12O6
Molecular Mass
Definition
The sum of masses of the atoms present in a molecule is called as molecular mass.
OR
It is the comparison that how mach a molecule of a substance is heavier
than 1/12th weight or mass of carbon atom.Example
The molecular mass of CO2 may be calculated as
Molecular mass of CO2 = Mass of Carbon + 2 (Mass of Oxygen)
= 12 + 2 x 16
= 44 a.m.u
Molecular mass of H2O = (Mass of Hydrogen) x 2 + Mass of Oxygen
= 1 x 2 + 16
= 18 a.m.u
Molecular mass of HCl = Mass of Hydrogen + Mass of Chlorine
= 1 + 35.5
= 36.5 a.m.u
Gram Molecular Mass
Definition
The molecular mass of a compound expressed in gram is called gram molecular mass or mole.
Examples
1. The molecular mass of H2O is 18. If we take 18 gm H2O then it is called 1 gm molecular mass of H2O or 1 mole of water.
2. The molecular mass of HCl is 36.5. If we take 36.5 gm of HCl then it is called as 1 gm molecular mass of HCl or 1 mole of HCl.
Mole
Definition
It is defined as atomic mass of an element, molecular mass of a compound or formula mass of a substance expressed in grams is called as mole.
OR
The amount of a substance that contains as many number of particles
(atoms, molecules or ions) as there are atoms contained in 12 gm of pure
carbon.Examples
1. The atomic mass of hydrogen is one. If we take 1 gm of hydrogen, it is equal to one mole of hydrogen.
2. The atomic mass of Na is 23 if we take 23 gm of Na then it is equal to one mole of Na.
3. The atomic mass of sulphur is 32. When we take 32 gm of sulphur then it is called one mole of sulphur.
From these examples we can say that atomic mass of an element expressed in grams is called mole.
Similarly molecular masses expressed in grams is also known as mole e.g.
The molecular mass of CO2 is 44a.m.u. If we take 44 gm of CO2 it is called one mole of CO2 or the molecular mass of H2O is 18a.m.u. If we take 18 gm of H2O it is called one mole of H2O.
When atomic mass of an element expressed in grams it is called gram atom
While
The molecular mass of a compound expressed in grams is called gram molecule.
According to the definition of mole.
One gram atom contains 6.02 x 1023atoms
While
One gram molecule contain 6.02 x 1023 molecules.
Molar Mass
The mass of one mole of a substance is called molar mass.
Example
1 mole of Hydrogen atom (H) = 1.008g
1 mole of Hydrogen molecule (H2) = 2.016g
Thus mass of substance is related to the particles by mole.
Avogadro’s Number
An Italian scientist, Avogadro’s calculated that the numbers of particles (atoms, molecules) in one mole of a substance are always equal to 6.02 x 1023. This number is known as Avogadro’s number and represented as NA.
Example
1 gm mole of Na contain 6.02 x 1023 atoms of Na.
1 gm mole of Sulphur = 6.02 x 1023 atoms of Sulphur.
1 gm mole of H2SO4 = 6.02 x 1023 molecules H2SO4
1 gm mole of H2O = 6.02 x 1023 molecules of H2O
On the basis of Avogadro’s Number “mole” is also defined as
Mass of 6.02 x 1023 molecules, atoms or ions in gram is called mole.
Determination Of The Number Of Atoms Or Molecules In The Given Mass Of A Substance
Example 1
Calculate the number of atoms in 9.2 gm of Na.
Given:
Mass of Na = 9.2 gm
Atomic mass of Na = 23 a.m.u
Number of Atoms = NA = ?
Solutions:
Using Formula
NA = mass of substance / molecular Mass x 6.02 x 1023
= 9.2 / 23 x 6.02 x 1023
= 2.41 x 1023 Atoms
Determination Of The Mass Of Given Number Of Atoms Or Molecules Of A Substance
Example 2
Calculate the mass in grams of 3.01 x 1023 molecules of glucose (C6H12O6).
Given:
Molecular mass of glucose = 180 a.m.u
Number of Molecules = NA = 3.01 x 1023 molecules
Mass of Glucose = ?
Solutions:
Using Formula
NA = mass of substance / molecular Mass x 6.02 x 1023
Mass of Glucose = NA x Molecular Mass / 6.02 X1023
= 3.01 x 1023 x 180 / 6.02 X1023
= 90 gm
Chemical Reaction
A chemical change in which reactants are converted to products is called chemical reaction.
Zn + 2HCl ——–> ZnCl2 +
H2
The fact that a chemical reaction is taking place can be inferred from the
following observation.1. Evolution of a gas
2. Change in colour
3. Change in temperature.
4. Emission of light.
Types of Chemical Reaction
The chemical reaction is classified into following types:
1. Displacement Reaction
The reaction in which an atom or group of atoms is displaced by another atom or group of atoms in a compound is called displacement reaction.
Fe + CuO ———> Cu + FeO
2. Double Displacement Reactions
The reactions in which reacting substances exchange their radicals or ions are double displacement reaction. Insoluble salts are formed by mixing soluble salts.
3. Addition Reactions
When two different compounds or elements react together to give only one confound, the reaction will be called addition reaction.
2Mg + O2 ——–> 2MgO
4. Decomposition Reaction
The reaction in which some compounds may decompose into elements or simpler compounds on heating is called decomposition reaction.
CaCO3 ———> CaO + CO2
(Heat)
Chemical Equation
Symbolic representation of chemical change in terms of symbols and formulae is called Chemical Equation.
Method of Equation Writing
A chemical equation can be written as follows:
1. Write the formulae and symbols of the reactants on the left hand side.
2. Write the formulae and sympols of the products on the right hand side.
3. Separate the reactants and products by an arrow which is directed towards the products.
Characteristics of Chemical Equation
1. Chemical equation must be representative of a chemical reaction.
2. It should represent molar quantities.
3. It should be balanced in terms of atoms/molecules of reactants and products.
Reactants
Those substances, which react together in a chemical reaction, are called reactants.
Zn + 2HCl ——> ZnCl2 + H2
In the above reaction Zn and HCl are the reactants.Products
Those substances, which are formed in a chemical reaction, are called products.
Zn + 2HCl ——> ZnCl2 + H2
In the above reaction, ZnCl2 and H2 are products.Information obtained from a Chemical Equation
1. A balanced equation indicates that which reactant undergo chemical change. It indicates that which products are formed.
2. It indicates that how many moles of reactants under go chemical change. It indicates that how many moles of products are formed.
Why are Chemical Equations Balanced
A chemical equation must be balanced in order to satisfy the law of conservation of matter, which states that matter can neither be created nor be destroyed during a chemical reaction.
Mass – Mass Relationship
In this relationship we can determine the unknown mass of a reactant or product from a given mass of the substance involved in the chemical reaction by using a balanced chemical equation.
Example
Calculate the mass of CO2 that can be obtained by heating 50 gm of limestone (CaCO3).
Solution
Step I (Write a Balanced Equation)
CaCO3 ——> CaO + CO2
Step II (Write Down The Molecular Masses And Moles Of
Reactant & Product)
CaCO3 ——> CaO + CO2
Method I – MOLE METHOD
Number of moles of 50 gm of CaCO3 = 50 / 100 = 0.5 mole
According to equation
1 mole of CaCO3 produce 1 mole of CO2
0.5 mole of CaCO3 produce 0.5 mole of CO2
Now,
We Know That
Mole = Mass of Substance / Molecular Mass
Therefore,
Mass of CO2 = Moles x Molecular Mass
= 0.5 x 44
= 22 gm
Method II – FACTOR METHOD
From equation we may write as
100 gm of CaCO3 gives = 44 gm of CO2
1 gm of CaCO3 will give = (44/100) gm of CO2
50 gm of CaCO3 will give = (50 x 44 / 100) gm of CO2
50 gm of CaCO3 will give = 22 gm of CO2