Some Gases

1. How is carbon dioxide prepared in the laboratory?
Ans: Carbon dioxide is prepared in the laboratory by the action of dilute hydrochloric acid on calcium carbonate.

2. Dilute sulphuric acid should not be used for the laboratory preparation of carbon dioxide gas. Why?
Ans: Dilute sulphuric acid should not be used for the laboratory preparation of carbon dioxide gas because calcium sulphate so formed being insoluble will cover the calcium carbonate and stops the reaction further.

3. Ammonia gas is collected in the gas jar by downward displacement of air. Why?
Ans: Ammonia gas is collected in the gas jar by downward displacement of air because it is lighter than air and highly soluble in water.

4. Draw a neat and labeled diagram showing laboratory preparation of ammonia gas. Also write the balanced chemical reaction of that gas formed.
Ans: 

In the laboratory, ammonia gas can be prepared by heating a mixture of ammonium chloride and calcium hydroxide in the ratio of 2:1 to yield calcium chloride, water and ammonia gas.

    2NH₄Cl           +            Ca(OH)₂    →   CaCl₂          +          2H₂0          +         2NH₃
Ammonium                       Calcium           Calcium                   Water                 Ammonia
chloride                            hydroxide         chloride
 
5. Write any four chemical properties of ammonia gas.
Ans: Four chemical properties of ammonia gas are as following:
i.    Ammonia is highly soluble in water to give ammonium hydroxide. The resultant solution of ammonium hydroxide, which is basic in nature.
NH₃           +        H₂O         →     NH₄OH
Ammonia       Water             Ammonium hydroxide

ii.    Since ammonia is basic gas it reacts gas so it reacts with acid to give salt. For example, ammonia gives ammonium chloride with hydrochloric acid.
NH₃      +      HCl    →                NH₄Cl
Ammonia        Hydrochloric            Ammonium
                                acid                       chloride

iii.    Ammonia reacts with carbon dioxide at 15000C to give urea.
2NH₃ +    CO₂           →               NH₂CONH₂     +     H₂O
Ammonia   Carbon dioxide                     Urea                 Water

iv.    Ammonia is a non-combustible gas and it does not support combustion but it burns in oxygen to give nitrogen and water.  

4NH₃          +       3O₂   →   6H₂O
Ammonia        Oxygen                 Water
 
6. What is ammonia?
Ans: Ammonia is a compound made up of nitrogen and hydrogen.

7. Ammonia gas cannot be collected by downward displacement of water. Why?
Ans: Ammonia gas cannot be collected by downward displacement of water because ammonia gas is highly soluble in water.

8. What happens when a glass rod dipped in conc. HCl is introduced in a jar containing ammonia gas?
Ans: When a glass rod dipped in conc. HCl is introduced in a jar containing ammonia gas, it produces white dense fumes of ammonium chloride.

9. What happens when ammonia gas is dissolved in water?
Ans: When ammonia gas is dissolved in water, ammonium hydroxide is formed.

10. What is slaked lime?
Ans: A white alkaline substance consisting of calcium hydroxide, made by adding water to quick lime is called slaked lime.

11. How is carbon dioxide prepared in the laboratory?
Ans: Carbon dioxide is prepared in the laboratory by the action of dilute hydrochloric acid on calcium carbonate.

12. Dilute sulphuric acid should not be used for the laboratory preparation of carbon dioxide gas. Why?
Ans: Dilute sulphuric acid should not be used for the laboratory preparation of carbon dioxide gas because calcium sulphate so formed being insoluble will cover the calcium carbonate and stops the reaction further.

13. What happens when carbon dioxide gas is dissolved in water?
Ans: When carbon dioxide gas is dissolved in water, carbonic acid is formed.

14. What happens when carbon dioxide is passed through lime water?
Ans: When carbon dioxide is passed through lime water, lime water turns milky due to the formation of white suspension of insoluble calcium carbonate.

15. What is dry ice?
Ans: The solid form of carbon dioxide is called dry ice.

16. What happens when carbon dioxide is continuously passed through lime water?
Ans: When carbon dioxide is continuously passed through lime water, the milky solution becomes clear due to the formation of soluble calcium bicarbonate.

17. What happens when the clear solution of calcium bicarbonate is boiled?
Ans: When the clear solution of calcium bicarbonate is boiled, calcium bicarbonate decomposes into calcium carbonate, water and carbon dioxide and the milkiness reappears due to the formation of calcium carbonate.

18. Carbon dioxide solution has acidic nature. Why?
Ans: Carbon dioxide solution has acidic nature because when carbon dioxide is dissolved in water, it forms carbonic acid which turns blue litmus paper into red.

19. Why carbon dioxide gas is collected in a gas jar by upward displacement of air?
Ans: Carbon dioxide gas is collected in a gas jar by upward displacement of air because carbon dioxide gas is heavier than air.

20. Why is carbon dioxide gas not collected in a gas jar by displacement of water?
Ans: Carbon dioxide gas is not collected in a gas jar by displacement of water because carbon dioxide gas is soluble in water.

21. Carbon dioxide gas is used to extinguish the fire. Why?
Ans: Carbon dioxide gas is used to extinguish the fire because it is neither combustible nor helps in combustion and being heavier than air it settles down on the burning surface and forms a layer cutting off the supply of oxygen to fire.

22. What is lime water?
Ans: Saturated solution of slaked lime in water is called lime water.

23. What is carbonation?
Ans: Carbonation is the phenomenon in which carbon dioxide gas is suspended in liquid, creating small bubbles.

24. What happens when ammonia reacts with carbon dioxide gas at 1500^oC under low pressure?
Ans: When ammonia reacts with carbon dioxide gas at 1500^oC under low pressure, urea, a nitrogenous fertilizer is produced.

25. What happens in each of the given conditions? Write the chemical equations.

i.   Carbon dioxide is passed into lime water for a while.
ii.  Carbon dioxide is passed into lime water for a long time.
iii. Carbon dioxide dissolves in water.
iv. Calcium bicarbonate is heated. 

Ans:
i.    When carbon dioxide is passed into the lime water for a while, it turns lime-water into milky white due to the formation of insoluble calcium carbonate.

                  CO₂          +         Ca(OH)₂             →      CaCO₃        +          H₂O
         Carbon Dioxide            Lime water                Calcium carbonate     Water
                             

ii.    When carbon dioxide is passed into lime water for a long time, it produces soluble bicarbonate. As a result of this, the milky white colour disappears.

                CaCO₃       +       H₂O      +     CO₂   →   Ca(HCO₃)₂ (Calcium bicarbonate)

iii.    Carbon dioxide gives carbonic acid (H2CO3) when it is dissolved in water.
                CO₂         +       H₂O  →    H2CO₃

iv.    When calcium bicarbonate is heated, calcium carbonate, carbon dioxide and water are formed.
                Ca(HCO₃)₂  →    CaCO₃          +      C0₂       +         H₂0
 
26. What is Haber’s process?
Ans: Haber’s process is the commercial method of producing ammonia in which a mixture of nitrogen and hydrogen (1:3) is heated at a temperature of 500^oC under 200-600 atmospheric pressure in the presence of iron as catalyst and molybdenum as promoter.

Class 9 Science: Carbon And It's Compounds

1. What is carbon?
Ans: Carbon is a non-metallic element which is present on the earth’s crust in free as well as in combined state.

2. What is meant by carbon?
Ans: A naturally abundant, non metallic element that occurs in all organic compounds and can be found in all known forms of life.

3. What are inorganic compounds?
Ans: The compounds which are obtained from minerals or inorganic sources are called inorganic compounds.

4. What are organic compounds?
Ans: The compounds which contain carbon and hydrogen combined together with other elements are called organic compounds.

5. What is organic chemistry?
Ans: The branch of chemistry in which we study about organic compounds is called organic chemistry.
Or
 A branch of chemistry that is concerned with carbon and especially carbon compounds which are found in living things.

6. What is water gas?
Ans: Water gas is a mixture of carbon monoxide and hydrogen produced by passing steam over hot carbon.

7. What are allotropes?
Ans: Different forms of an element which exists in different physical forms with slightly different chemical properties are called allotropes.

8. Why is carbon a reactive non-metal?
Ans: Carbon is a reactive non-metal because it combines with many other elements.


9. What is diamond?
Ans: Diamond is one of the hardest allotrope of carbon which is transparent, brilliant and more precious.

10. What is graphite?
Ans: Graphite is soft slippery, black and greasy allotrope of carbon.

11. What is coal?
Ans: Coal is an amorphous allotrope of carbon which is formed in nature as a result of the slow decomposition of organic matter under influence of heat and pressure and limited supply of air

12. How is wood charcoal made?
Ans: Wood charcoal is made by the destructive distillation of wood.

13. How is animal charcoal made?
Ans: Animal charcoal is made by the destructive distillation of degreased bones in iron retorts.

14. What is allotropy?
Ans: The property of an element to exist in different physical forms with slightly different chemical properties is called allotropy.

15. What is co-valency?
Ans: The number of electron pairs which an atom shares to acquire a stable condition is called co-valency.

16. What is a caramel?
Ans: The brown substance with good smell formed on heating sugar is called caramel.

17. What is an inorganic chemistry?
Ans: The branch of chemistry which deals with the study of inorganic compounds is called inorganic chemistry.

18. What is catenation?
Ans: The property of carbon due to which its atom forms a long chain by combining with one another is called catenation.


19. Write any three sources of carbon?
Ans: Some of the main sources of carbon are as follows:
• In air, carbon dioxide is found.
• Various petroleum products.
• In all living organisms, in substances like carbohydrate, starch, urea etc.

20. How does carbon exist in nature?
Ans: Carbon occurs in two forms in nature. They are as follows:
• Free State: Carbon exists as free state in the forms of Graphite, Diamond.
• Combined state: Carbon combines with other elements to form compounds such as carbon dioxide, glucose etc.

21. Write any two properties of carbon.
Ans:
 • Carbon has several allotropes or different forms in which it can exist.
• Carbon has ability to make four bonds and is present in many compounds.

22. Write any three chemical properties of carbon with balanced chemical equations.
Ans: 

• When carbon is heated with oxygen, and then carbon dioxide gas is formed.

                                        C + O₂      →     CO₂

• When carbon is heated with less oxygen, then carbon monoxide is formed.

                                        2C + O₂    →     2CO

• When carbon is heated with lead oxide, then carbon dioxide is given out.

                                       C + 2PbO   →   CO₂ + 2Pb

23. What is catenation? Write in brief with an example.
Ans: The property of carbon due to which its atoms form a long chain by combining with one another is called catenation.
Carbon is the most common element that exhibits catenation. It can form long hydrocarbon chains and rings like benzene.

24. What is water gas?
Ans: A fuel gas consisting mainly of carbon monoxide and hydrogen, made by passing steam over incandescent coke.

25. What happens when:

Carbon is heated in water vapour?

Ans: When carbon is heated with water vapor, then carbon monoxide and hydrogen gas are formed.
C + H₂O → CO + H₂



26. Apart from the organic beings, where else do we find carbon? Mention the form in which it is available there and also its percentage.
Ans: Carbon is found in atmosphere and earth’s crust. Carbon is found as CO₂ in atmosphere and as minerals in earth’s crust. The percentage of carbon in air is 0.03℅ and in earth’s crust about 0.02℅.

27. What is allotropy? Write all the allotropes of carbon.
Ans: Allotropy is phenomena of forming elements having same chemical properties but differing in physical properties. Allotropes of carbon:
• Diamond
• Graphite
• Fullerene

28. Write any four amorphous forms of carbon.
Ans: Amorphous forms of carbon are as follows:
• Charcoal
• Coal
• Coke
• Lampblack

29. What are the properties of diamond?
Ans: The properties of diamond are as follows:
• Colourless transparent substance with extraordinary brilliance due to its high refractive index.
• It's quite heavy.
• It's extremely hard. (Hardest substance known)
• It's doesn't conduct electricity. (Due to absence of free ions)
• It has high thermal conductivity and high melting point.
• It burns on strong getting to form carbon dioxide.





30. Enlist the uses of diamond.
Ans: The uses of diamond are listed below:
• It is used as a precious gem in jewelers.
• It used for cutting glass and marble, black diamond (carbonate) and for boring or drilling on rocks.
• It is used to make a high quality thermometer.
• It is used to make radiation proof windows for spacecraft.

31. What is another name of graphite?
Ans: Plumbago or black lead is another name of graphite.

32. Write the uses of graphite.
Ans: The uses of graphite are as follows:
• The major use of graphite is in making lead pencils of different hardness,
• The presence of free electrons makes graphite a good conductor of electricity and it is used to make electrodes.
• It is used as lubricants.

33. What are the properties of graphite?
Ans: The properties of graphite are as follows:
• It's a greyish black, opaque substance.
• It's lighter than diamond, feels soft and slippery to touch.
• It's good conductor of electricity (due to presence of free ions) but bad conductor of heat.
• On strong heating, it burns to give carbon dioxide.
• It’s insoluble in water and organic solvents

34. What is the reason behind the soft and slippery nature of graphite?
Ans: The different layers of carbon atoms in graphite are held together by weak Vander Waals force of attraction and these layers can slide over each other and makes graphite soft and slippery.

35. Write the uses of fullerene.
Ans: The uses of fullerene are as follows:
• Fullerenes may be used for drug delivery systems in the body and as lubricants.
• It takes part in catalytic processes.
• Used as a therapeutic and diagnostic agent.
• Acts as a potential inhibitor to HIV.

36. Why is fullerene so called?
Ans: Fullerene resembles the framework of dome shaped halls designed by American architect Buckminster fuller so called as fullerenes.

37. What are the properties of fullerenes?
Ans: Properties of fullerenes:
• Fullerenes are stable, but not totally nonreactive.
• Fullerenes are soluble in many solvents like CO₂.
• Fullerenes are the only known allotrope of carbon that can be dissolved in common solvents at room temperature like C28, C36 etc.

38. What is the formula of buckyball?
Ans: The formula of buckyball is C₆₀.

39. What is Mho?
Ans: Mho is a unit which is used to measure hardness of the substances.

40. What is soot?
Ans: Lampblack/ black substance formed after burning carbon compounds.

41. State vital force theory?
Ans: According to vital force theory, formation of organic compounds takes place only under the influence of some which is present in the living organism only.

42. What is sugar charcoal?
Ans: Sugar charcoal is a black coloured substance which is formed by heating sugar caramel continuously.

43. Write the differences between:

Diamond and Graphite

Ans: 

Diamond	Graphite
It is the hardest  substance  known.	It is soft and slippery.
It is transparent and  colourless substance with bright appearance.	It is an opaque, dark grey and shiny.
It is a bad conductor of heat and electricity.	It is a good conductor of heat and electricity.
Its specific gravity is 3.5.	Its specific gravity is 2.2.

44. Write the differences between: 

Organic compounds and Inorganic compounds

Ans: The differences between organic compound and inorganic compound are as follows:

Organic compounds	Inorganic compounds
They are insoluble in water.	They are soluble in water.
They have low melting and boiling point.	They have high melting and boiling point.
They have covalent bonds and cannot be electrolyzed.	They are formed by electrovalent bonds and can undergo electrolysis.
They are soluble in organic solvents.	They are insoluble in organic solvents.

45. Write the differences between:

Ionic compounds and covalent compounds

Ans: The differences between ionic compounds and covalent compounds are as follows:

Ionic compounds	Covalent compounds
They are formed by transfer of electrons.	They are formed by sharing of electrons.
They generally exist in solid form. e.g. NaCl.	They may be solid (I2), liquid(Br2) or gas(Cl2).
Conducts electricity in molten state.	They do not contain ions so they are bad conductor of electricity.
They have high melting points and boiling points.	They have low melting points and boiling points.

44. Define:

Caramel

Ans: Caramel is brunt sugar used for colouring and adding flavor to food.

45. Give reasons:

Carbon forms covalent bonds.

Ans: Carbon forms covalent bonds to gain stability, it should lose its valence electrons, gain four more electrons or share its 4 valence electrons with other atoms.

46. Give reasons:

Diamond is a bad conductor while graphite is a good conductor of electricity.

Ans: It is because in graphite, carbon forms covalent bonds with only three carbon atoms and there is one free electron in each carbon atom but diamond does not have free electrons.

47. Give reasons:

Graphite is used as lubricant.

Ans: Graphite is used as lubricant because it is soft and non-volatile.

48. Give reasons:

Diamond is the hardest substance known.

Ans: Diamond is the hardest substance known because each carbon atom in diamond is joined to four other carbon atoms giving rise to a three dimensional rigid and a stable structure.

49. Give reasons:

Carbon is a reducing agent.

Ans: Carbon is a reducing agent because it separates metals from their concerning metallic oxide when it is heated with the metallic oxides.
C + CuO        →          Cu + CO
C + PbO        →          Pb + CO

52. Give reasons:

Organic compounds are non- electrolyte.

Ans: Organic compounds are non electrolyte because they are covalent compounds and they do not dissociate into ions in their molten state and aqueous form.

53. Give reasons:

Compounds like Na₂CO₃, CaCO₃, etc. are not organic compounds even though they have carbon.

Ans: It is because they are electrovalent compounds and only covalent compounds having carbon are considered as organic compounds.[CO₂ and CO are covalent and have carbon but traditionally they are considered as inorganic ].

54. Give reasons:

Molecular formula of calcium carbide is CaC₂not Ca₂C.

Ans: It is because calcium losses two electrons to form the molecule as it is a metal. The electrons are received by two carbon atoms and they also share three electrons between them.

55. What happens when:

Lead oxide is strongly heated with carbon?

Ans: Carbon dioxide is formed separating metal.
2PbO + C    →    2Pb + CO₂

56. Define:

Organic compounds

Ans: The compounds which contain carbon and hydrogen combined together with other elements are called organic compounds.

57. Define:

Tetravalency

Ans: Tetravalencey is the state of an atom with four valence electrons available for covalent chemical bonding in its outermost electron shell.

58. Define:

Inorganic compounds

Ans: The substances derived from minerals are called inorganic compounds.

BLE Science: Matter

1. What is an atom?
Ans: An atom is the smallest particle of an element which can take part in a chemical reaction.

2. What is atomic number?
Ans: The number of electrons or the number of protons in an atom is called atomoic number.

3. What is an atom?
Ans: An atom is the smallest particle of an element which can take part in a chemical reaction.

4. What is atomic number?
Ans: The number of electrons or the number of protons in an atom is called atomoic number.

5. What is atomic mass?
Ans: The sum of protons and electrons in an atom is called atomic mass.

6. What is electronic configuration?
Ans: The distribution of electrons in different orbits is called electronic configuration.

7. What is a molecule?
Ans: A molecule is the smallest particle of a substance which exists independently.

8. What does the Modern period law states?
Ans: Modern period law states that the properties of elements are the period function of their atomic number.

9. What is chemical change?
Ans: A permanent change in which new substances are formed is called chemical change.

10. What are periods?
Ans: The horizontal rows in a periodic table are called periods.

11. What is compound?
Ans: A compound is the pure substance formed by the chemical combination of two or more elements in a fixed proportion.

12. What is physical change?
Ans: Physical change is a temporary change in which no new substance is formed.

13. What are groups?
Ans: The vertical columns of the period table are called groups.

14. What is Mendeleev period law?
Ans: Mendeleev period law states that “the physical and chemical properties of the elements are the periodic functions of their atomic masses”.

15. What is proton?
Ans: Proton is the smallest particle that has a unit of positive electric charge.

16. What is neutron?
Ans: Neutron is the chargeless particle which is situated at the nucleus of an atom.

17. What is molecular weight?
Ans: The sum of the atomic weights of all the atoms of the same or different elements present in a molecule is called molecular weight.

18. What is period table?
Ans: The systematic arrangement or classification of all the elements on the basis of their similar properties in the tabular form is called periodic table.

19. An atom is electrically neutral. Why?
Ans: An atom is electrically neutral because the number of protons is equal to the number of electrons.

20. What is classification of elements?
Ans: The grouping of elements according to their similar characteristics is called classification of elements.

21. What are the differences between atom and molecule?
Ans: The differences between atom and molecule are;
 

	Atom	Molecule
Definition	An atom is the smallest particle of an element which can take part in a chemical reaction.	A molecule is the smallest particle of an element or a compound that can exist independently.
Weight	The atomic weight of an atom is the sum of total number of protons and neutrons present in the atom. It is called atomic weight.	The molecular weight of a molecule is the sum of atomic weight of the atoms present in the molecule. It is called molecular weight.

22. What are the differences between neutron and proton?
Ans: The differences between neutron and proton are;
 

	Neutron	Proton
Definition	A neutron is a neutral sub-atomic particle which is present inside the nucleus of an atom.	A proton is a positively charged sub-atomic particle which is present inside the nucleus of an atom.
Charge	A neutron is neutral, so it has no charge. The charge in neutron is equal to 0 coulombs.	A proton is positively charged. The charge in a proton is equal to 1.60×10-19 coulombs.

23. What are the differences between neutron and electron?
Ans: The differences between neutron and electron are;
 

	Neutron	Electron
Definition	A neutron is a neutral sub-atomic particle which is present inside the nucleus of an atom.	An electron is a negatively charged sub-atomic particle which is present outside the nucleus of an atom; it is in the shell of an atom.
Denotation	A neutron is usually denoted by no.	An electron is usually denoted by n-.
Charge	A neutron is neutral, so it has no charge. The charge in a neutron is equal to 0 coulombs.	An electron is negatively charged. The charge in an electron is equal to – 1.60 ×10-19 coulombs.
Mass	The mass of a neutron is equal to 1 amu; which is equal to 1.67 × 10-24grams.	The mass of an electron is equal to 1/1837 amu; which is equal to 9.1 × 10-28 grams.

24. What are the differences between proton and electron?
Ans: The differences between proton and electron are;
 

	Proton	Electron
Definition	A proton is a positively charged sub-atomic particle which is present inside the nucleus of an atom.	An electron is a negatively charged sub-atomic particle which is present outside the nucleus of an atom; it is in the shell of an atom.
Denotation	A proton is usually denoted by p+.	An electron is usually denoted by n-.
Charge	A proton is positively charged. The charge in a proton is equal to 1.60×10-19 coulombs.	An electron is negatively charged. The charge in an electron is equal to – 1.60 ×10-19 coulombs.
Mass	The mass of a proton is equal to 1 amu; which is equal to 1.67 × 10-24 grams.	The mass of an electron is equal to 1/1837 amu; which is equal to 9.1 × 10-28 grams.

25. What are the differences between molecule of an element and molecule of a compoud?
Ans: The differences between molecule of an element and molecule of a compound are;
 

	Molecule of an element	Molecule of a compound
Definition	A molecule of an element is the molecule that is formed by the combination of only one type of atoms.	A molecule of compound is the molecule that is formed by the combination of two or more different types of atoms.
Example	N2 is the molecule of nitrogen. O2 is the molecule of oxygen. And so on.	NH3 is the molecule of ammonia. H2O is the molecule of water. And so on.

26. What are the differences between element and compound?
Ans: The differences between element and compound are;
 

	Element	Compound
Definition	Element is defined as the purest substance that contains only one type of atoms.	Compound is defined as the purest substance that contains two or more different types of atoms.
Nature	An element cannot be broken down into simpler substances by any chemical methods.	A compound can be separated into simpler substances by any chemical methods.

27. What are the differences between electropositive radical and electronegative radical?
Ans: The differences between electropositive radical and electronegative radical are;
 

	Electropositive radical	Electronegative radical
Definition	Electropositive radical is defined as a radical having positive charges.	Electronegative radical is defined as a radical having negative charges.
Type	Electropositive radical is also called basic radical or metallic radical.	Electronegative radical is also called acidic radical or non-metallic radical.

28. What are the differences between Mendeleev’s periodic table and modern periodic table?
Ans: The differences between Mendeleev’s periodic table and modern periodic table are;
 

	Mendeleev’s periodic table	Modern periodic table
Definition	The table which is obtained by arranging elements on the basis of their increasing atomic mass is called Mendeleev’s periodic table.	The table which is obtained by arranging elements on the basis of atomic number is called modern periodic table.
Statement of law	Mendeleev’s law states, “Physical and chemical properties of elements are the periodic function of their atomic mass.”	Modern periodic law states, “Physical and chemical properties of elements are the periodic function of their atomic mass.”
Periods and groups	In Mendeleev’s periodic table, there are 7 horizontal rows; called periods and 8 vertical columns; called groups.	In modern periodic table, there are 7 horizontal rows; called periods and 18 vertical columns; called groups.
Nature	Mendeleev’s periodic table could not explain the valency or metallic characteristics.	Modern periodic table explained the gradual change in valency and the metallic characteristics of different elements; metals, non-metals and metalloids.

29. What are the differences between physical change and chemical change?
Ans: The differences between physical change and chemical change are;
 

	Physical change	Chemical change
Definition	The change in which the chemical composition of a substance remains the same is called physical change.	The change in which the chemical composition of a substance alters i.e. altered is called chemical change.
Properties	Physical change in a substance does not form any new substance, only the physical properties of the substance changes.	Chemical change in a substance forms new substance with entirely different chemical properties from before.
Nature	Physical change is a temporary change; it can be reversed easily.	Chemical change is a permanent change; it cannot be reversed easily.
Example	Melting of ice and boiling of water are some of the examples of physical change.	Rusting of iron and burning of wood are some examples of chemical change.

30. What is the difference between radical and compound?
Ans: The difference between radical and compound is;

	Radical	Compound
Definition	Radical is defined as an atom or group of atoms that act as a single unit having positive or negative charges on it.	Compound is defined as the purest substance that contains two or more different types of atoms.

31. What is the difference between chemical reaction and chemical equation?
Ans: The difference between chemical reaction and chemical equation is;
 

	Chemical reaction	Chemical equation
Definition	The exchange, combination or decomposition that occurs in the molecules of matters during a chemical change is called chemical reaction.	The symbolic representation of the chemical change in a chemical reaction in terms of symbols or formulae is called chemical equation.

32. What are the differences between radical and compound?
Ans: 

		Radical	Compound
1.	Definition	Radical is defined as an atom or group of atoms that act as a single unit having positive or negative charges on it.	Compound is defined as the purest substance that contains two or more different types of atoms.

33. What are the differences between chemical reaction and chemical equation?
Ans: 

		Chemical reaction	Chemical equation
1.	Definition	The exchange, combination or decomposition that occurs in the molecules of matters during a chemical change is called chemical reaction	The symbolic representation of the chemical change in a chemical reaction in terms of symbols or formulae is called chemical equation.

34. Calculate the molecular weight of chalk. Write two advantages of Mendeleev's periodic table.
Ans: Here,
We have,
Atomic weight an atom = number of proton + number of neutron
Molecular weight of an compound = sum of masses of the combining atom
Molecular formula of chalk is CaCO₃
Again,
Atomic weight of calcium (Ca) = 20 + 20 = 40 amu
Atomic weight of carbon (C) = 6 + 6 = 12 amu
Atomic weight of oxygen (3O) = 3 (8 + 8) = 48 amu
Finally,
Molecular weight of chalk (CaCO₃) = 40 + 12+ 48 = 100 amu
Hence, molecular weight of chalk is 100 amu.

Advantages of Mendeleev's periodic table are as followings:
I.    Systematic study of elements 
In Mendeleev's periodic table, elements were classified in such a way that the elements with similar properties came to lie in the same vertical column. This helped in systematic study of elements.
II.    Prediction of new elements
Mendeleev's periodic table helped in discovery of new element.
 
35. Draw the well labelled atomic stucure of the element having atomic number 18 and also write the valency of same element.
Ans: Argon is the element having atomic number 18. Its valency is 0, because its outer shell is already filled with 8 electrons and it does not combine with other atoms.




36. Calculate atomic weight of CaCO₃. Define periodic table and why it is constructed?
Ans: Here,
Atomic weight of calcium (Ca) = 20 + 20 = 40 amu
Atomic weight of carbon (C) = 6 + 6 = 12 amu
Atomic weight of oxygen (3O) = 3 (8 + 8) = 48 amu
We have,
Molecular weight of CaCO₃ = 40 + 12+ 48 = 100 amu
Hence, molecular weight of CaCO₃ is 100 amu.

The systematic arrangement of all the elements on the basis of their properties is called periodic table.

Periodic table is constructed due to following reasons:
I.    It helps us to memorize the characteristics of large number of elements in the form of few groups only.
II.    New elements of known properties can be predicted.

37. What are the subatomic particles? What does 2n² rule indicate?
Ans: Atoms are made up of three fundamental particles: electron, proton and neutron. These are called subatomic particles.
2n² rule indicates maximum number of electrons in different shell (K, L, M, N.....) of an atom.
 
38. What is octet? Mention the number of groups and period in modern periodic table.
Ans: Presence of 8 electrons in valence shell of an atom is termed as octet. There are 18 groups and 7 periods present in the modern periodic table.

39. Differentiate between electron and proton by two points. What is electric charge?
Ans: Differences between electrons and protons are as followings.

Protons	Electrons
They are positively charged particles.	They are negatively charged particles.
They are found in nucleus.	They revolve around nucleus.

 Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field.


40. Write the number of electrons, protons and neutrons of an element having atomic number 19. What is valency and write the valency of that atom.
Ans: The element having atomic number 19 is potassium (K)
Number of electrons = 19
Number of protons = 19
Number of neutrons = 20
The combining capacity of an element or radical with other element or radical to form molecule or compound is called valency.
Valency of potassium is 1.

41. Define octet rule. What is the molecular formula of Aluminium oxide?
Ans: The natural tendency of an atom of an element to make 8 electrons in its valence shell by gaining, losing or sharing electrons between the combining atoms during the formation of molecules is called octet.

The molecular formula of magnesium oxide is MgO.

42. Who was the inventor of periodic table? What is compound? Why water is called compound?
Ans: The inventor of modern periodic table is Henery Moseley.
A substance made from the chemical reaction of two or more atoms of elements in a fixed proportion by weight is called compound.
Water is called as compound because it is made from chemical reaction of hydrogen and oxygen atom in a fixed proportion by weight.

43. What is orbit? Generally, atom is assumed that it is chargeless, why?
Ans: The path traced by electrons around the nucleus is called orbit.
In an atom, positively charged protons and neutral neutrons are found in nucleus while negatively charged electrons revolve around nucleus in a fixed path i.e. orbit. As number of protons and number of electrons in an atom are equal and positive charge of proton and negative charge of electron cancel each other, atom is assumed chargeless.

44. 

Study the given table and answer the following questions.

Group	IA	IIA	IIIA	IVA	VA	VIA	VIIA	O
Period2	Li	Be	X	C	N	O	F	Ne
Period3	Na	Mg	Al	Si	P	S	Cl	Y

i. Write the name of elements X and Y.
ii. Why zero group elements inert gas and elements of group VIIA are most reactive in periodic table?

Ans: 
i. X - Boron (B)
   Y - Argon (Ar)
ii. Zero group elements have 8 electron is their valence shell (except Helium has 2 electrons in it valence shell). As their valence shell is already filled, they do no need to lose or gain electron i.e. they do not take part in chemical reaction. Hence, due to their stable electronic configuration, zero group elements are called inert gas.
Group VIIA elements have 7 electrons in their valence shell. They need only one electron to fulfill their octet. So, they easily gain one electron from other atom during chemical reaction and acquire unit negative charge. Hence, group VIIA elements are very active.
 
45. Write any one advantage of periodic table. Draw atomic structure of chlorine atom.
Ans: Advantage of periodic table-
It helps us to memorize the characteristics of large number of elements in the form of few groups only.


 Fig: Atomic structure of chlorine

46. Write any one difference between mixture and compound. Mention the charge of proton and electron.
Ans: Difference between mixture and compound is as following:

Mixture	Compound
A mixture is a material made up of two or more different substances which are mixed but are not combined chemically.	A substance made from the chemical reaction of two or more atoms of elements in a fixed proportion by weight is called compound.

Proton contains positive charge while electrons contain negative charge.

47. Calculate the number of protons, neutrons and electrons of the element having atomic mass 39. Write the molecular formula of ammonia.
Ans: The element having atomic mass 39 is Potassium (K).
Number of electrons = 19
Number of protons = 19
Number of neutrons = 20
The molecular formula of ammonia is NH_⁴.

 48. By what name Group IA elements are denoted? The valency of nitrogen is 3, clarify it.
Ans: Group IA elements are also known as alkali metals. The valency of nitrogen is 3. This means that combining capacity of nitrogen is 3. The number of electron present is valence shell of nitrogen is 5. So, it gains 3 more electrons from other atom during chemical reaction to form stable electronic configuration.

49. The element chlorine has atomic number 17 and atomic mass 35, calculate the number of protons, neutrons and electrons. Write one difference between octet and duplet rule.
Ans: Number of electrons = Atomic number = 17
Number of protons = Atomic number = 17
Number of neutrons = Atomic mass — Number of protons
                                 = 35-17
                                 = 18
Difference between octet rule and duplet rule is as following:

Octet rule	Duplet rule
The natural tendency of an atom of an element to make 8 electrons in its valence shell by gaining, losing or sharing electrons between the combining atoms during the formation of molecules is called octet.	The natural tendency of an atom of an element to make 2 electrons in its valence shell by gaining, losing or sharing electrons between the combining atoms during the formation of molecules is called duplet.

50. Who is the developer of modern periodic table? On which basis it is made? Valency of argon is zero. Why?
Ans: The developer of modern periodic table isHenery Moseley. Modern periodic table is made on the basis of atomic number of elements.
Argon has 8 electrons in its valence shell. As its valence shell is already filled, it has stable electronic configuration. It does no need to lose or gain electron i.e. it does not take part in chemical reaction. Hence, argon has valency 0.

51. What is chemical equation? Hydrogen and oxygen react to give water, write the word equation and chemical equation for it.
Ans: A chemical reaction which is expressed by using molecular formulae of reactants and products is called chemical equation.
Word equation-
Hydrogen + Oxygen →  Water
Chemical equation-
2H₂ + O₂ → 2H₂O

52. Write the molecular formula of magnesium chloride. What is inert gas? Write with an example.
Ans: The molecular formula of magnesium chloride is MgCl₂.
Those elements which have 8 electrons in their valence shell (except Helium, it has 2 electrons) and have no tendency to combine with other elements are termed as inert gas.
For example- Helium, Neon and Argon.

Class 9: Trigonometry (Compound Angles)

The proved trigonometric statements are also benificial to the students of 10th standard also...


1. Prove that: 
Tan(A + B) = TanA+TanB1-TanA TanB . 
Proof: LHS = Tan(A + B)
         = Sin(A + B)Cos(A + B)  
       = SinACosB+CosASinBCosACosB - SinASinB
        =  SinACosBCosACosB+ CosASinBCosACosBCosACosBCosACosB-SinASinBCosACosB   [ ∵ Dividing Numerator & denominator by CosACosB & seperating LCM.]
      =TanA+TanB1-TanA TanB
       = RHS.
                    Proved.

2. Prove that : 

Tan(A - B) =TanA-TanB1+ TanA TanB

Proof: Here, 
LHS  = Tan(A - B) 
        =Sin(A - B)Cos(A - B)
        =SinACosB - CosASinBCosACosB + SinASinB 
        = SinACosBCosACosB- CosASinBCosACosBCosACosBCosACosB+SinASinBCosACosB   [ Dividing numerator & denominator by CosACosB.]
       =TanA-TanB1+TanA TanB
        = RHS.

Proved.

3. Prove that: 

Cot(A + B)  =CotACotB-1CotB+CotA .

Proof: LHS = Cot(A + B)
        = Cos(A+B)Sin(A+B)
       =CosACosB- SinASinBSinACosB + CosASinB 
       =   CosACosB SinASinB- SinASinBSinASinBSinACosBSinASinB+CosASinBSinASinB  [∵ Dividing numerator and denominator by SinASinB & Seperating LCM.]
      = CotACotB-1CotB+CotA
       = RHS.

Proved.

Alternatively, you can also prove it by the formula of tan(A+B).

4. Prove that:

 Cot(A - B)  =CotACotB+1CotB-CotA .

Proof: LHS = Cot(A-B)
       =Cos(A-B)Sin(A-B) 
      =CosACosB+SinASinBSinACosB - CosASinB
     = CosACosB SinASinB+ SinASinBSinASinBSinACosBSinASinB-CosASinBSinASinB [ ∵ Dividing numerator & denominator by SinASinB & seperating LCM.]
    =CotACotB+1CotB-CotA
     = RHS.

Proved.

Alternatively, you can also prove it by the formula of tan(A-B).

5. Prove that: 

Sin(A+B).Sin(A-B) = Cos²B - Cos²A.

Proof: LHS = Sin(A+B).Sin(A-B)
         = ( SinACosB + CosASinB)(SinACosB - CosASinB)
         = (SinACosB)² - (CosASinB)²
         = Sin²ACos²B - Cos²ASin²B
         = ( 1- Cos²A)Cos²B - Cos²A(1 - Cos²B)
         = Cos²B - Cos²ACos²B - Cos²A + Cos²ACos²B
         =  Cos²B - Cos²A.
         = RHS.

Proved.

6. Prove that : 

Sin(A+B).Sin(A-B) = Sin²A - Sin²B.

Proof: Here,
LHS = sin ( A + B ) ⋅ sin ( A − B )
        = ( sinA cosB + cosA sinB ) ( sinA cosB − cosA sinB )
        = ( sinA cosB )² − ( cosA sinB )²    [Using the identity ( p + q ) ( p − q ) = p ² − q ² .]
        = sin²A cos²B − sin²B cos²A
        = sin²A ( 1 − sin²B ) − sin²B ( 1 − sin²A )
        = sin²A − sin B − sin²A sin²B + sin²B sin²A
        = sin²A − sin²B.
        = RHS.

Proved.

7. Prove that : 

cos(A+B).cos(A-B) = Cos²A - Sin²B.

Proof: Here,
LHS =  cos(A+B).cos(A-B)
        = (cosAcosB - sinAsinB)(cosAcosB +sinAsinB)
        = (cosAcosB)² - (sinAsinB)²
        = cos²Acos²B - sin²Asin²B
        = Cos²A( 1 - Sin²B) - (1 - cos²A)Sin²B
        = Cos²A - Cos²ASin²B - Sin²B + cos²ASin²B
        = Cos²A - Sin²B.
        = RHS 

Proved.

8. Prove that: 

cos(A+B).cos(A-B) = cos²B - sin²A.

Proof: Here,
LHS =  cos(A+B).cos(A-B)
        = (cosAcosB - sinAsinB)(cosAcosB +sinAsinB)
        = (cosAcosB)² - (sinAsinB)²
        = cos²Acos²B - sin²Asin²B
        = cos²B( 1 - cin²A) - (1 - cos²B)cin²A
        = cos²B - cos²Bsin²A - sin²A + cos²Bsin²A
        = cos²B - sin²A.
        = RHS.

Proved.

9. Prove that: 

cot(A+B).cot(A-B)  =Cot²ACot²B-1Cot²B-Cot²A .

Proof: LHS = cot(A+B).cot(A-B)
        = CotACotB-1CotB+CotA⨉CotACotB+1CotB-CotA
       = (CotACotB-1)(CotACotB +1)(CotB+CotA)(CotB - CotA)
       =Cot²ACot²B-1Cot²B-Cot²A
        = RHS.

Proved.

10. Prove that: 

tan(A+B).tan(A-B) = tan²A-tan²B1-tan²Atan²B   .

Proof: LHS = tan(A+B).tan(A-B)
                 =tanA+tanB1-tanAtanB⨉tanA-tanB1+tanAtanB
                 =tan²A-tan²B1²-(tanAtanB)²
                 =tan²A-tan²B1-tan²Atan²B  
                 = RHS.

Proved.

11. Find the value of cos15^o without using calculator or table.
Solution: We know,
 Cos15^o = cos(45^o - 30^o)
              = cos45^ocos30^o + sin45^osin30^o
              = 1√2⨉ 
√32  + 12 ⨉1√2 
            
 = √3+12√2
Which is required value of cos15^o.

12. If A+B = π^c/4, prove that: 

cotAcotB - cotA - cotB = 1.

Proof: We know, π^c = 180^o
So, A+B = 45^o
Operating both sides by cot we get
      cot(A+B) = cot45^o    , using formula of cot(A+B), we get
⇒ cotAcotB-1cotB+cotA = 1          [ Since, cot45^o = 1.]
⇒ cotAcotB - 1 = cotB + cotA
⇒ cotAcotB - cotA - cotB = 1
       LHS = RHS.

Proved.

Next method :
LHS = cotAcotB - cotA - cotB
        = 1 + [cotAcotB - 1] - cotA - cotB
   = 1 + [cotB + cotA] × cotAcotB-1cotB+cotA  - cotA - cotB
   = 1 + [cotB + cotA] × cot(A+B) - cotA - cotB
   = 1 + [cotB + cotA] × 1 - cotA - cotB 

 [cot(A+B) = cot(π^c/4) = 1]

   = 1 + cotB + cotA] - cotA - cotB
   = 1 

Proved

13. Prove that: 
sin105° + cos105° = 1√2  
Proof: Here,
 LHS = sin105° + cos105°
         = sin(60^o + 45^o ) + cos ( 60^o + 45^o )
         = ( sin 60^o cos 45^o + cos 60^o sin 45^o ) + ( cos 60^o cos 45^o - sin60^o sin 45^o)
         =  √32 . 1√2 + 12 . 1√2 +  12 . 1√2 -  √32 . 1√2 


 
         = 22√2 
       = 1√2  
       = RHS.

Proved.

14. Prove that:  cot73^o.cot28^o+1cot73^o-cot28^o  = 1
Proof: LHS = cot73^o.cot28^o+1cot73^o-cot28^o  
    = cot(73^o -28^o) [ Since, cotA.cotB+1cotB-cotA = cot(A-B).]
    = cot45^o
    = 1
     = RHS.

Proved.

15. Prove that: 

cot27^o.cot18^o - cot27^o- cot18^o = 1

Proof: Here,
We know,
      27^o + 18^o = 45^o
Operating both side by cot,we get
      Cot(27^o+18^o) = cot45^o
⇒ cot27^o.cot18^o-1cot27^o+cot18^o = 1       
[ Since, using formula of cot(A+B) & cot45^o = 1.]
⇒ cot27^o.cot18^o - 1 = cot27^o + cot18^o
⇒ cot27^o.cot18^o- cot27^o - cot18^o = 1
i.e.  LHS = RHS

Proved.

Next method :
LHS = cot27°cot18º - cot27º - cot18º
        = 1 + [cot27ºcot18º - 1] - cot27º - cot18º
   = 1 + [cot27º + cot18º] × cot27ºcot18º-1cot27º+cot18º  - cot27º - cot18º
    = 1 + [cot27º + cot18º] × cot(18º+27º) - cot27º - cot18º
   = 1 + [cot27º + cot18º] × 1 - cot27º - cot18º 
   = 1 + cot27º + cot18º - cot27º - cot18º
   = 1 

Ptoved

16. Prove that: tan50^o + tan60^o + tan70^o = tan50^o.tan60^o.tan70^o.

Proof: Here,
     50^o + 60^o + 70^o = 180^o
⇒ 50^o + 60^o = 180^o - 70^o
Operating both sides by tan, we get
     tan(50^o + 60^o) = tan(180^o - 70^o)
⇒  tan50^o +tan60^o1 - tan50^o.tan60^o = - tan70^o        [ Since, using formula of tan(A+B) & tan(180^o- A) = -tanA.]
⇒ tan50^o + tan60^o = -tan70^o(1 - tan50^o.tan60^o)
⇒ tan50o + tan60^o = -tan70^o + tan50^o.tan60^otan70^o 
⇒ tan50^o + tan60^o + tan70^o = tan50^o.tan60^otan70^o 
∴  LHS = RHS

Proved.

17. Prove that: tan9A - tan6A - tan3A = tan9A.tan6A.tan3A.
Proof: Here,
     3A + 6A = 9A
Operating both sides by tan, we get
     tan( 3A + 6A) = tan(9A)
⇒ tan3A + tan6A1 - tan3A.tan6A = tan9A  [ Since, using formula of tan(A+B).]
⇒ tan3A + tan6A = tan9A(1 - tan3A.tan6A)
⇒ tan3A + tan6A = tan9A - tan3A.tan6A.tan9A 
⇒ tan9A - tan6A - tan3A = tan9Atan6Atan3A.
∴  LHS = RHS

Proved.

18. Prove that : sin(x+y) + sin(x-y) = 2sinxcosy.
Proof: Here,
LHS = sin(x+y) + sin(x-y)
         = sinxcosy + cosxsiny + sinxsiny - cosxcosy
         = sinxcosy + sinxcosy
         = 2sinxcosy
         = RHS.

Proved.

19. If A+B+C = π^c & cosA = cosBcosC, prove that tanA =  tanB + tanC.
Proof: LHS = tanA 
        = sinAcosA
       =sin[π -(B+C)])cosBcosC       [∵ A= π - (B+C) & cosA = cosBcosC.]
       = sin(B+C)cosBcosC
       = sinBcosC + cosBsinCcosBcosC
       = sinBcosCcosBcosC +  cosBsinCcosBcosC
       =sinBcosB +  sinCcosC 
       = tanB + tanC
       = RHS.

Proved.

20. An angle θ is divided into two parts α & β such that  tanα : tanβ = x : y, then prove that:
sin(α-β)  = x-yx+ysinθ      
Proof:   Here, we have given
     tanα : tanβ = x : y.
⇒  tanαtanβ =  xy 
By using componendo & dividendo , we have
       tanα + tanβtanα - tanβ = x+yx - y
Converting into sin & cos we get
     sinαcosβ + cosαsinβsinαcosβ - cosαsinβ = x + yx - y
⇒   sin(α+β)sin(α - β) = x+yx - y
⇒  sinθsin(α-β) = x+yx - y               [ Since, α+β = θ.]
⇒ sin(α-β)  = x-yx+ysinθ          

Proved.                       

21. Prove that:  
sinA + sin(A+2π3) + sin(A+ 4π3) = 0
Proof: Here,
LHS = sinA + sin(A+2π3) + sin(A+ 4π3)     
Now, put π = 180^o, we get
        = sinA + sin(A+ 120^o ) + sin(A+  240^o )     
        = sinA + sinAcos120^o + cosAsin120^o + sinAcos240^o+cosAsin120^o
        = sinA + sinA(- 12) + cosA(√32) + sinA(- 12) + cosA(-√32)
        = sinA - 12 sinA - 12 sinA
        = sinA - sinA
        = 0
       = RHS

Proved.

22. sin²(π6 + θ) - sin²(π6 - θ)  = √32 sin2θ 
Proof: Here, 
LHS = sin²(π6 + θ) - sin²(π6 - θ)  
        = sin²( 30^o + θ) - sin²( 30^o - θ)                 
[ Since, π = 180^o.]
        = sin(30^o+θ + 30^o-θ) . sin(30^o+θ-30^o+θ)       
 [ Since, sin²A - sin²B = sin(A+B).sin(A-B).]
        = sin60^o .sin2θ
        = √32 sin2θ 
        = RHS

Proved.

23. If tanA = 56 & tanB=2π3, prove that prove that,
A+B =  π^c4 
Proof: We know,
 tan(A+B) = tanA+tanB1 - tanAtanB
                 = 56+1111- 56×111
                 =56665666
                 = 1
                 = tan45^o
 tan(A+B) = tan π4 
  So, A+B =  π^c4 

Proved.

24. 

In any quadrilateral ABCD, prove that  

cosAcosB - cosCcosD =  sinAsinB - sinCsinD.

Proof: We know,
           ABCD is a quadrilateral.
Then
      A+B+C+D = 360^o 
⇒  A+B = 360 - (C+D)
Operating both sides by cos,
     cos(A+B) = cos{360 -(C+D)}         
Using formula,we get
⇒ cosAcosB - sinAsinB = cosCcosD - sinCsinD    [ Since, cos(360 -θ) = cosθ.]
⇒  cosAcosB - cosCcosD =  sinAsinB - sinCsinD
      LHS = RHS

Proved.