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NEW TRENDS IN ICSE CHEMISTRY - 8

CHAPTER - 9 . Carbon and Its Compounds

Tick (✔) The correct choice amongest the following

1. Carbon monoxide burns with : (a) No flame(b) Yellow flame(c) Blue flame(d) Red flame

2. For combustion reactions :(a) Air is essential(b) Combustible substance is essential(c) Both (a) and (b)(d) Neither (a) nor (b)

3. Which of the following is not an amorphous form of carbon ?(a) Coal(b) Charcoal(c) Diamond(d) Lamp black

4. Charcoal is :(a) Crystalline carbon(b) Amorphous carbon(c) Both of these(d) None of these

5. Soot is :(a) Lamp black(b) Charcoal(c) Coke(d) Graphite

6. Diamond is :(a) Soft(b) Slippery in nature(c) Hardest known substance(d) None of these

7. The weight of diamond is expressed in :(a) Carat(b) Milligram(c) Grams(d) None of these

8. Water gas is :(a) CO + H2(b) CO2 + H2(c) CO + H(d) None of these

9. Graphite is used :(a) As a lubricant(b) In making electrodes(c) In lead pencils(d) All of these

10. Allotropy is shown by :(a) Hydrogen(b) Carbon(c) Both (a) and (b)(d) None of these

Fill in The Blanks

1. The property of self linking of carbon atoms is known as .................... .

2. Radioactive isotope of carbon is .................... .

3. One carat is equal to .................... grams.

4. Diamonds shine because of high .................... .

5. Black diamonds contain .................... in them.

6. .................... is the hardest substance known.

7. .................... and .................... are the two major allotropes of carbon.

8. The atoms in a diamond are arranged in .................... manner.

9. When wood is heated in the absence of air the residue is called .................... .

10. The allotropic forms are physically .................... but chemically .................... .

Write True or False for each statment.Rewrite the Statement Correctly

1. Fullerenes have C10 and C20 carbon number.

2. Diamond is the hardest known substance.

3. Wood charcoal is also known as animal charcoal.

4. Lamp black, soot and kajal all are same.

5. Adsorption is a surface phenomenon.

6. The word ‘graphite’ comes from a greek word meaning ‘to write’.

7. Charcoal has higher calorific value than wood.

8. Charcoal is a good adsorbent.

Match The Columns

1. 1.Destructive distillation of wood2.Pigment in black boot polish3.Dehydration of sugar4.Metallurgical operations sugar charcoalcokelamp blackcharcoal

Answer The Followings Questions

1. Write the symbols of the three isotopes of carbon.

2. Which isotope is used to find the age of prehistoric objects ?

3. Name one important component of “printers ink”.

4. Define the term allotropy.

5. Name the three common allotropes of carbon.

6. Give an equation to show burning of diamonds.

7. Why diamond sparkles ?

8. Name the impurity present in Emerald.

9. Why is diamond known to be the hardest substance ?

10. Graphite conducts electricity whereas diamond does not. Explain.

11. How will you prove that coal, diamond and graphite all are allotropes of carbon ?

12. Where do van der Waals’ forces operate ?

13. Why are diamonds used in space probes ?

14. Why is graphite used for making lead pencils ?

15. Give any four uses of fullerenes.

16. Define destructive distillation.

17. How is sugar charcoal prepared ?

18. Why is carbon black used in tyres ?

19. Explain charcoal cavity test.

20. How will you prove that powdered charcoal act as a reducing agent ?

21. What is activated charcoal ?

22. Draw and explain the structure of :(i) diamond (ii) graphite.

23. Write a short note on fullerenes.

Answers

Tick (✔) The correct choice amongest the following

1. (c) Blue flame

2. (c) Both (a) and (b)

3. (d) Lamp black

4. (b) Amorphous carbon

5. (a) Lamp black

6. (c) Hardest known substance

7. (a) Carat

8. (a) CO + H2

9. (b) In making electrodes

10. (b) Carbon

Fill in The Blanks

1. catenation

2. C-14

3. 0.2

4. refractive index

5. copper oxide

6. Diamond

7. Diamond, graphite

8. tetrahedral

9. wood charcoal

10. different, same

Write True or False for each statment.Rewrite the Statement Correctly

1. False (Fullerness have C60 carbon number)

2. True

3. False (Bone charcoal is also known as animal charcoal)

4. True

5. True

6. True

7. True

8. True

Match The Columns

1. 1.charcoal

2.lamp black

3.sugar charcoal

4.coke

Answer The Followings Questions

1. C-12, C-13, C-14

2. C-14

3. Carbon

4. The phenomenon of existence of a chemical element in two or more forms differing in physical properties but having almost same chemical nature is known as allotropy. There different forms are called allotropes.

5. Diamond, graphite and coal

6. C + O2 ----> CO2

(Diamond)

7. Diamond has a high refractive index of 2.415. Due to its high refractive index, it undergoes total internal reflection and appears sparkling.

8. Emerald has a green colour which is due to the presence of small traces of chromium oxide.

9. Diamond is the purest and hardest form of carbon. Its structure forms a giant molecule where each carbon atom is surrounded by four other carbon atoms. So, each carbon atom is located in the centre of a regular tetrahedron. This network of carbon atoms extends in three dimensions and provides it a very rigid structure.

10. Graphite has got free electron in its structure which makes it a good conductor whereas diamond has no free electrons in its structure, hence it does not conduct electricity.

11. If you burn all the three allotropes, all will form the same end product i.e., carbon dioxide.

12. Between the layers of graphite, there exists a weak force of attraction called van der Waal's force. These layers are able to slide over one another.

13. Diamonds are used in space probes as it can keep out harmful radiations.

14. Graphite is used for making lead pencils because of its ability to leave mark on paper.

15. Fullerenes are used as

(i) Super conductors

(ii) Semi conductors

(iii) Lubricants

(iv) Catalysts

16. The process of heating wood in the absence of air, in order to decompose into smaller fragments, is known as destructive distillation.

17. Sugar charcoal is prepared by the destructive distillation of sugar. It can also be obtained by dehydrating sugar with concentrated sulphuric acid.

18. Carbon black is used as filler in rubber tyres to make it hard and strong.

19. Take a small piece of charcoal block and make a fine hole (cavity) in the centre of it. Take small amount ofred mercury oxide and put it into the fine hole on charcoal. The hole is known as cavity and this test is known as charcoal cavity test.

By using blow pipe, direct the luminous flame of bunsen burner to the cavity.

After sometime red mercury oxide turns to silvery grey globule of metallic mercury.

This indicates that mercury oxide is reduced to the metal mercury.

20. Take a long test tube. Fill it with ammonia gas and invert it over a trough containing mercury as shown in the fig. Now, introduce a small piece of activated charcoal in the test tube over mercury. You will observe that the level of mercury rises which indicates that the gas has been adsorbed by charcoal.

21. We can improve the activity of charcoal by heating it to 900° C to 950° C in absence of air and then passing steam through it. This charcoal is changed to activated charcoal. The steam increases the size of the pores. So, its adsorbing property increases 10 times than normal.

This activated charcoal is used in filters to remove offensive smell from air ; colouring matter, foul odour, bad taste and toxic chemicals from water.

22. (a) Diamond is the purest and hardest form of carbon. Its

structure forms a giant molecule where each carbon atom is surrounded by four other carbon atoms. So, each carbon atom is located in the centre of a regular tetrahedron.

This network of carbon atoms extends in three dimensions and provides it a very rigid structure.

(b) In graphite, each carbon atom is linked to three other carbon atoms forming hexagonal rings stacked one on other. Within these layers, each carbon atom is bonded to three others by strong covalent bonds. The fourth electron is free and accounts for the electrical conductivity. Between the layers, there are weak forces of attraction due to which the layers can easily slide over each other making graphite soft, slippery and useful as a lubricant.

23. Fullerene is a naturally occurring allotrope of carbon in which 60 carbon atoms are linked to form a stable structure. The molecular structure looks like a football or the domed roof of the stadium developed by American engineer Buckminster Fuller. Thus, it was named as Buckminsterfullerene. It is often called bucky ball for short.

It is a yellow powder and is soluble in organic solvent. It is a non-conductor and preferably an electric insulator. It is more reactive than diamond and graphite.

CARBON AND ITS COMPOUNDS

EXERCISES

A. ANSWER THE FOLLOWING QUESTIONS IN ABOUT TWENTY WORDS.

Q. 1. Describe the self-linking property of carbon.

Ans. Carbon has a unique property by virtue of which it forms

regular covalent bonds with other carbon atoms almost infinitely. This

self-linking property of carbon leading to the formation of long chains and

rings of carbon atoms is called catenation or self-linking.

It is due to this property of catenation (self-linking), that carbon forms

a large number of compounds (about 5 million).

Q. 2. Write the chemical equations describing the burning of

carbon under the following conditions.

(a) In excess of air (b) In limited supply of air.

Ans. (a) Carbon burns in excess of oxygen/air to give carbon dioxide.

burning

C(s) + O2

(g) → CO2

(g) + Heat + Light

Carbon From air Carbon dioxide (As flame)

(Excess supply)

(b) In a limited supply of oxygen/air, carbon burns to forms carbon

monoxide.

burning

2C(s) + O 2

(g) → 2CO(g) + Heat + Light

Carbon From air Carbon monoxide

(Limited supply)

Q. 3. Give any three differences between the properties of

diamond and graphite.

2 TEACHER’S MANUAL :: The World of Science–CHEMISTRY— 8

Ans. The differences between the properties of diamond and graphite

are as follows :

Diamond Graphite

Diamond occurs naturally in a free

state.

Graphite occurs naturally, and also

manufactured artificially.

Diamond is transparent and has high

refractive index (2.45).

Graphite is black in colour and is

opaque.

Diamond occurs as octahedral

crystals.

Graphite occurs as hexagonal

crystals.

Q. 4. Give reactions to show that carbon is a reducing agent.

Ans. Carbon (in the form of coke) acts as a reducing agent. It reduces

certain metal oxides to the corresponding metals.

It reduces CuO to Cu.

heat

2CuO(s) + C(s) → 2Cu(s) + CO 2

(s)

Copper oxide Coke Copper Carbon dioxide

It reduces lead oxide (PbO) to lead (Pb).

heat

2PbO(s) + C(s) → 2Pb(l) + CO 2

(g)

Lead oxide Coke Lead Carbon dioxide

Q. 5. What is meant by allotropy ? Name the two allotropes

of carbon.

Ans. The property by virtue of which an element can exist in

more than one forms is called allotropy. Diamond and graphite are two

allotropic forms of carbon.

Q. 6. Carbon has two allotropes — diamond and graphite.

Explain why is diamond a poor conductor, while graphite is a

good conductor of electricity.

Ans. In diamond, each carbon atom is covalently bonded to four

other carbon atoms in a tetrahedral fashion. This tetrahedral arrangement

of carbon atoms gives a rigid, three-dimensional structure to diamond.

It is due to this rigid, three-dimensional structure that diamond is a

nonconductor of heat and electricity.

In graphite, carbon atoms are arranged in flat parallel layers. Each

carbon atom in these layers is bonded to three others by covalent bonds

forming a network of six-carbon rings. The fourth valence electron of each

carbon is free to move.

Due to this, graphite is a good conductor of electricity.

Q. 7. Write a short note on the structure of graphite. Account

for one of its properties from the structure.

Ans. Refer Ans. 6 above.

Q. 8. Write a short note on the structure of diamond. Why is

diamond so hard ? Explain this in terms of its structure.

Ans. In diamond, each carbon atom is covalently bonded to four

other carbon atoms in a tetrahedral fashion. This tetrahedral arrangement

of carbon atoms gives a rigid, three-dimensional structure to diamond.

Structure of diamond

It is due to this rigid, three-dimensional structure that diamond is is

very hard.

Q. 9. Give any three differences between the properties

of diamond and graphite. Explain why do they differ in their

properties ?

Ans. Refer Ans. 3 above for the differences between the properties

of diamond and graphite.

They differ in their properties because of the difference in their

structure.

For the structure of diamond and graphite refer Ans. 6 and Ans. 8.

Q. 10. How is charcoal obtained from wood ? Draw a

labelled diagram of the apparatus used.

Ans. Charcoal or wood charcoal is obtained from wood. Wood

on heating in the absence of air, loses volatile components and moisture,

and gets converted into charcoal.

The conversion of wood into charcoal can be described by the

following chemical equation.

heat strongly,

absence of air

Wood → Charcoal + Volatile matter + Moisture

(Black residue) Escape into

the air

CARBON AND ITS COMPOUNDS 3

4 TEACHER’S MANUAL :: The World of Science–CHEMISTRY— 8

The breakdown of a substance by heating strongly in the absence of

air is called destructive distillation.

Laboratory preparation of charcoal from wood

Q. 11. Give reactions to show that carbon is a

(a) reducing agent

(b) combustible substance.

Ans. (a) Refer Ans. 4 above.

(b) Refer Ans. 2 (a) or 2 (b).

B. TICK (4) THE CORRECT CHOICE.

1. Different forms of the same element which differ only in their

physical properties are called

(a) allotropes (b) isomers

2. Which of the following is the purest form of carbon ?

(a) Charcoal (b) Graphite

3. The source rock of diamond is

(a) phosphorite (b) sedimentary

4. The compounds of carbon and hydrogen are called

(a) carbohydrates (b) hydrocarbons

5. Carbon forms a very large number of compounds becasue, it is

capable of forming

(a) ionic bonds

(b) multiple bonds

(d) all types of bonds

6. Which of the following is a good conductor of electricity ?

(a) Lamp black (b) Coke

Ans. 1. (a) 2. (c) 3. (d) 4. (b) 5. (c) 6. (c)

C. FILL IN THE BLANK SPACES IN THE FOLLOWING STATEMENTS.

1. Diamond is a crystalline form of carbon.

2. Pencil lead is made from graphite.

3. Lamp black, charcoal, and coal are the amorphous forms of

carbon.

4. Buckminster fullerene molecule contains 60 atoms of carbon.

5. The variety of coal containing the minimum percentage of carbon

is peat.

6. Carbon occurs in nature in the elemental form as diamond.

7. Carbon atoms in diamond are bonded to each other by

covalent bonds.

8. The gas formed when carbon is burnt in an insufficient supply of

air is carbon monoxide.

9. The gas which turns limewater milky is carbon dioxide.

D. WRITE T FOR TRUE AND F FOR FALSE STATEMENT.

1. Diamond is a good conductor of electricity.

2. Gas masks are based on the principle of adsorption of gases by

charcoal powder.

3. Carbon dioxide is more dangerous than carbon monoxide.

4. Indian ink is made from lamp black.

5. Gas carbon is a good conductor of electricity.

6. Carbon monoxide can be used as a fuel.

CARBON AND ITS COMPOUNDS 5

6 TEACHER’S MANUAL :: The World of Science–CHEMISTRY— 8

7. The molecules C 60 is called Buckminister fullerene.

8. Carbon is an oxidising agent.

Ans. 1. False 2. True 3. False 4. True 5. True

6. True 7. True 8. False

E. ENCIRCLE THE ODD-ONE FROM THE LISTS GIVEN BELOW.

1. Carbon dioxide, Limestone, Dolomite, Calcium carbide,

Hydrogen sulphide.

2. Methane, Ethane, Butene, Propane.

3. Coke, Wood charcoal, Sugar charcoal, Lamp black, Fullerene.

4. Diamond, Graphite, Fullerene, Charcoal powder.

Ans. 1. Hydrogen sulphide, others contain carbon.

2. Butene, others are saturated carbon compounds.

3. Fullerene, others are amorphous forms of carbon.

4. Charcoal powder, others are crystalline forms of carbon.