CARBON AND CARBON COMPOUNDS

14. CARBON AND CARBON COMPOUNDS

14 CARBON AND CARBON COMPOUNDS

points to remember :

1. Carbon is a non-metallic element. Carbon is the main

constituent of all plant and animal products. In nature, it is

found in the free state as diamond and graphite and also in

compounds. Carbon is present in air as carbon dioxide, as also in

fuels like biogas, petroleum and marsh gas.

2. Anthracite, Bituminous coal, Lignite, Peat are the different

types of coal.

3. Allotropes : Some elements are found in nature in more than

one form. They have same chemical properties but different

physical properties. These forms are called allotropes of an

element. Carbon exhibits allotropy in two forms – crystalline and

amorphous form. Diamond, graphite and fullerene are

crystalline allotropes while coke, coal are amorphous allotropes.

4. Carbon dioxide : Carbon dioxide occurs in free state in

atmospheric air. It is found in chalk, Shahabad stone and

limestone in compound form. Carbon dioxide is prepared in the

laboratory from calcium carbonate and hydrochloric acid.

Carbon dioxide is a tasteless, odourless and colourless gas. It is

heavier than air and sparingly soluble in water. Carbon dioxide

neither burns nor supports burning. It is used in the

manufacture of aerated cold beverages, dry ice, washing soda

and sodium bicarbonate (baking powder). It is used as fire

extinguisher. Plants use carbon dioxide to make their own food.

5. Methane : Methane is the first in the series of hydrocarbon

compounds. The molecular formula of methane is CH

_

. Methane

molecule has one carbon atom and four hydrogen atoms. It is

formed in marshy lands, therefore methane is called marsh gas.

In the laboratory, methane is produced by heating a mixture of

hydrogen and carbon monoxide to 300 °C in the presence of

catalyst nickel.

Methane is an odourless, tasteless and colourless gas. It is

lighter than air and insoluble in water. Methane is highly

inflammable and burns with a blue flame. It is used as a fuel. It is

used in the production of acetylene.

Questions and Answers

Q. 1 Answer the following questions :

(1) Where does carbon occur in nature ?

Ans. Carbon is the main constituent of all plant and animal

products. Carbon is a non-metallic element. In nature, it is found in

the free state as graphite and diamond and also in compounds.

Carbon is present in air as carbon dioxide, as also in fuels like

biogas, petroleum and marsh gas.

(2) How did coal form in nature ?

Ans. Plants and animals constantly receive solar energy.

Millions of years ago the remains of plants and animals got buried

under the earth. Due to action of microorganisms, the gaseous

substances in these remains were released into the atmosphere

and the left behind was carbon compounds. After this, under

tremendous pressure, the liquid substances in these compounds

drained away and the remaining mineral solidified into compact

and hard rock and this material is called coal.

(3) State the types of coal with the percentage of carbon

in it.

Ans. The types of coal with the percentage of carbon are as

follows :

Types of coal Percentage of carbon

(1) Anthracite 80

(2) Bituminous coal 60

(3) Lignite 22

(4) Peat 11

Answer to the Question given on page 136 of the textbook

What common feature is there in sugar, paper,

plastic, wood, cereals, pulses and petrol ?

Ans. They are all carbon compounds.

* (4) What is meant by allotrope ?

Ans. Some elements are found in nature in more than one

form. They have same chemical properties but different physical

properties. These forms are called allotropes of an element.

(5) In how many forms does carbon exhibit allotropy ?

Explain with suitable examples.

Ans. Carbon exhibits allotropy in two forms : crystalline form

and amorphous form. (1) In the crystalline form, the atoms of

the element have a specific arrangements. Example : diamond,

graphite and fullerene. (2) In the amorphous form, the

arrangement of atoms is irregular. Example : coke, coal, etc.

(6) Write the properties of diamond.

Ans. (1) Pure diamond is brilliant and an extremely hard

substance. (2) It is a bad conductor of electricity. (3) When

diamond is heated to a high temperature, it gives out carbon

dioxide. (4) Acids and alkalies do not have any effect on diamond.

Answers to the Questions given on page 137 of the textbook

* (1) What makes a diamond shine ?

Ans. A diamond is cut such that, it has number of faces,

therefore, the light rays entering the diamond undergo

multiple internal reflections before coming out. Therefore,

it shines.

* (2) What is the main difference between diamond and

glass ?

Ans. Diamond is in crystalline form while glass is in

amorphous form. The refractive index of diamond is much

higher than that of ordinary glass. Diamond is very hard while

glass is brittle.

* (3) Where are the diamond mines in India located ?

Ans. The diamond mines in India are located at Panna in

Madhya Pradesh.

 (7) Write the properties of graphite.

Ans. (1) The graphite that occurs in nature is black, soft and

smooth. (2) It is a good conductor of heat and electricity.

(8) Give the uses of graphite.

Ans. (1) Graphite is used in pencils for writing on paper.

(2) Graphite is used as positive electrode in dry cells. (3) Graphite

is used as lubricant. (4) For bright light, graphite is used in arc

lamps.

* (9) Why is graphite used as lubricant ?

Ans. A lubricant is used to reduce friction among the moving

parts of a machine. Due to the specific arrangement of carbon atoms

in a crystal of graphite it is soft and smooth. Hence, graphite is used

as a lubricant.

Answers to the Questions given on page 139 of the textbook

* (1) Which coal is used for purifying water?

Ans. Porous charcoal is used for purifying water.

* (2) Why is charcoal brittle ?

Ans. When carbon-rich plant material is burnt in

insufficient supply of oxygen, the hydrogen, nitrogen and

oxygen escapes. The end product is black and porous. As a

result charcoal becomes brittle.

* (3) Why is charcoal used as a domestic fuel ?

Ans. Charcoal burns with a smokeless flame. Hence, it is

used as a domestic fuel.

(10) Write the different sources of carbon dioxide.

Ans. (1) Carbon dioxide occurs in free state in atmospheric

air. (2) It is produced in respiration of plants and animals. (3) It is

found in chalk, Shahabad stone and limestone in compound form.

How to prepare Carbondioxide in the laboratory?_

Ans. (1) Some pieces

of calcium carbonate

(lime-stone) is taken in a

flat bottom flask. Set up

the apparatus as shown

in the diagram. The flask

is fitted with a two-holed

cork, bearing thistle

funnel. (2) Hydrochloric

acid is slowly added

through the thistle

funnel. Ensure that the lower end of the thistle funnel is immersed

in the hydrochloric acid. (3) A chemical reaction takes place

between calcium carbonate and hydrochloric acid and the carbon

dioxide gas is gradually evolved. The gas is then collected in gas jars

by the upward displacement of air.

 (

(13) Give the physical properties of carbon dioxide.

Ans. (1) Carbon dioxide is a tasteless, odourless and

colourless gas. (2) It is heavier than air. (3) It is sparingly soluble

in water. (4) Carbon dioxide neither burns nor supports burning.

Answer to the Question given on page 140 of the textbook

* What happens when lemon juice spills on the marble

kitchen counter?

Ans. (1) Marble is a form of calcium carbonate. (2) When

lemon juice (Citric acid is present in lemon juice) spills on the

marble (calcium carbonate), a chemical reaction takes place

between them and carbon dioxide gas evolves.

(14) Give the uses of carbon dioxide. OR

* Give two uses of carbon dioxide.

Ans. (1) Carbon dioxide is used in the manufacture of aerated

cold beverages. (2) It is used to produce dry ice. (3) It is used to

make washing soda. (4) It is used to produce sodium bicarbonate

(baking powder). (5) It is used as a fire extinguisher. (6) Plants use

carbon dioxide to make their own food.

Answers to the Questions given on page 142 of the textbook

* (1) Why do food preparations become light and crisp

when baking soda is used ?

Ans. When baking soda is used in the preparation of food,

carbon dioxide is released on heating. It escapes in the form

of bubbles. Therefore, the food preparations become porous,

light and crisp.

* (2) What is caustic soda ? Where is it used ?

Ans. Caustic soda is sodium hydroxide. It is used in the

production of soap and paper.

(15) Give two methods of preparation of methane.

Ans. (1) Methane is produced anaerobically (in the absence of

air) from plant and animal waste in a biogas plant.

(2) In the laboratory, methane is produced by heating a

mixture of hydrogen and carbon monoxide to 300°C in the presence

of catalyst nickel.

 (16) Give the properties of methane.

Ans. (1) Methane is an odourless, tasteless and colourless gas.

(2) Methane is lighter than air and insoluble in water. (3) Methane

is highly inflammable and burns with a blue flame.

* (17) Give the uses of methane.

Ans. (1) Methane is used as a fuel. (2) It is used to prepare

acetylene, another carbon compound.

Answers to the Questions given on page 144 of the textbook

* (1) Is carbon dioxide always formed when a hydrocarbon

is burnt?

Ans. Yes, carbon dioxide is always formed when a

hydrocarbon is burnt.

* (2) What is the difference between methane and the

gas in the cylinder we use at home?

Ans. The gas in the cylinder we use at home is butane

(also propane). It is liquefied under pressure. Methane cannot

be liquefied even under pressure.

Q. 2 Write notes on the following : (1) Diamond

(2) Graphite (3) Fullerene (4) Fire extinguisher.

Ans. (1) Diamond : (1) Millions of years ago, brilliant and

pure diamonds were formed by the crystallisation of carbon under

tremendous pressure. (2) In the diamond crystal, each carbon

atom is linked to four other carbon atoms at specific distance.

 (3) Brilliant, pure diamond is the hardest known substance. (4) It is

a bad conductor of electricity. (4) When it is

heated to a very high temperature, it gives out

carbon dioxide. (5) It does not react with acids

or alkalies. (6) When pure carbon is subjected

to extreme high pressure and very high

temperature, synthetic diamonds are formed.

(7) Diamond is used, as an ornament, to cut

glass and in drilling machines.

Fig. 14.3 : Graphite

(2) Graphite : (1) Graphite is a hexagonal

crystal. (2) Six carbon atoms form a hexagon

and are at specific distances from each other.

Thus, the regular arrangement of atoms in

graphite is in layers. (3) Within each layer,

every carbon atom has three other carbon

atoms around it at equal distances. (4) The

graphite is black, soft and smooth and it is a good conductor of

heat and electricity. (5) It is used in pencils. (6) It is used as positive

electrode in dry cells. (7) It is used as a lubricant. (8) It is used in

arc lamps for bright light.

Fig. 14.4 : Fullerene

(3) Fullerene : (1) Fullerene is allotrope

of carbon in which sixty carbon atoms are

linked to form a stable structure. (2) C

__

atoms

are joined to each other in pentagonal and

hexagonal arrangements. As a result, the

structure of Fullerene is exactly like a football.

(3) The properties of Fullerene are still being

studied. Scientists believe that Fullerene may prove of great use in

research related to superconductivity.

(4) Fire extinguisher : The fire extinguisher consists of a

cylinder filled with a solution of sodium bicarbonate. A capsule

containing dilute sulphuric acid is placed inside the cylinder. When

the knob is pressed, the sulphuric acid in the capsule spills on the

sodium bicarbonate, a chemical reaction takes place and carbon

dioxide is produced. Carbon dioxide is not combustible and does not

support combustion. Hence, it is used as a fire extinguisher.

Q. 3 Explain the following reactions, giving their

balanced equations :

(1) 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 insoluble calcium

carbonate.

oxide reacts with carbon dioxide.

Ans. When calcium oxide reacts with water, calcium

carbonate is formed.

 (3) Carbon dioxide is passed through water.

Ans. When carbon dioxide is passed through water, it

dissolves sparingly forming carbonic acid.

 (4) Carbon dioxide is passed through a solution of sodium

hydroxide.

Ans. When carbon dioxide is passed through a solution of

sodium hydroxide, sodium carbonate is formed.

 (5) Carbon dioxide is passed through a solution of sodium

carbonate.

Ans. When carbon dioxide is passed through a solution of

sodium carbonate, sodium bicarbonate is formed.

 (6) A mixture of hydrogen and carbon monoxide is heated

to 300°C.

Ans. When a mixture of hydrogen and carbon monoxide is

heated to 300°C, methane is formed.

 (7) Methane is burnt in air.

Ans. When methane is burnt in air, it burns with a blue flame

forming carbon dioxide.

in air.

Ans. When carbon is burnt in air, it combines with oxygen to

form carbon dioxide.

 (9) Sodium bicarbonate is treated with sulphuric acid.

Ans. When sodium bicarbonate is treated with sulphuric acid,

sodium sulphate and carbon dioxide gas is formed.

 (10) Calcium carbonate is treated with hydrochloric acid.

Ans. When calcium carbonate is treated with hydrochloric

acid, calcium chloride, water and carbon dioxide is formed.

Q. 4 Give scientific reasons :

* (1) Diamond is used to cut metals.

Ans. (1) Diamond is a crystalline allotrope of carbon. The

atoms in a crystalline form have a specific arrangement. (2) Since

diamond is the hardest substance it is used to cut metals.

* (2) Carbon dioxide is used for putting out fires.

Ans. (1) Carbon dioxide is not combustible and does not

support combustion. (2) It is heavier than air. (3) When it is spread

on a burning object, it covers the object and separates it from air.

Thus, the fire is extinguished. Hence, carbon dioxide is used for

putting out fires.

(3) Marble tiles are not used in kitchen.

Ans. (1) Marble is a form of calcium carbonate. (2) Calcium

carbonate reacts with an acid to form the corresponding calcium

salt and carbon dioxide gas. (3) In the kitchen, we use acidic

substance like lemon, tamarind, buttermilk, etc. These substances

may react with marble and the surface become rough. Hence,

marble tiles are not used in kitchen.

* Q. 5 Distinguish between the following :

(1) Crystalline form of carbon and Non-crystalline or

amorphous form of carbon :

Ans. Crystalline form of

carbon

Non-crystalline or amorphous

form of carbon

1. The atoms of carbon in a

crystalline form have a

specific arrangement.

1. The atoms of carbon in noncrystalline

form have

irregular arrangement.

2. Carbon in crystalline form is

an extremely hard material.

2. Carbon in non-crystalline

form is brittle.

(2) Diamond and Graphite :

Ans. Diamond Graphite

1. Diamond is an extremely

hard material.

1. Graphite is black, soft and

smooth.

2. In the diamond crystal, each

carbon atom is linked to four

other carbon atoms at

specific distances.

2. In graphite, six carbon atoms

form a hexagon and are at

specific distances from each

other. Within each layer

every carbon atom has three

other carbon atoms around it

at equal distances.

3. Diamond is a bad conductor

of electricity.

3. Graphite is a good conductor

of electricity.

4. It is used, as an ornament,

to cut glass and in drilling

machines.

4. It is used as lubricant.

Q. 6 Answer the following questions in one sentence

each :

(1) State atomic number, atomic mass number and

valency of carbon.

Ans. Atomic number of carbon : 6

Atomic mass number of carbon : 12

Valency of carbon : 4.

(2) Name a coal that contains highest percentage of

carbon.

Ans. The coal that contains highest percentage of carbon is

anthracite.

(3) Name the naturally occurring allotropic elements.

Ans. Carbon, sulphur, phosphorus are some of the naturally

occurring allotropes of carbon.

* (4) Which are the allotropes of carbon?

Ans. The diamond, graphite, fullerene, coke, coal are the

allotropes of carbon.

(5) Name the crystalline forms of carbon.

Ans. The diamond, graphite and fullerene are crystalline

forms of carbon.

(6) How were diamonds formed?

Ans. Millions of years ago, diamonds were formed by the

crystallization of carbon under tremendous pressure.

(7) How are synthetic diamonds made?

Ans. Synthetic diamonds are made by subjecting pure carbon

to extremely high pressure and heating it to a very high

temperature.

(8) State the shape of graphite crystal.

Ans. A graphite crystal is hexagonal.

* (9) How is charcoal made?

Ans. Charcoal is made by burning substances of plant origin

such as wood in an insufficient supply of oxygen.

(10) Name the compounds of carbon.

Ans. Chalk, Shahabad stone and limestone are some

compounds of carbon.

 Give two uses of carbon.

Ans. (1) Graphite is a crystalline form of carbon. It is used

(i) in pencils for writing on paper (ii) as a lubricant. (2) Coke is an

amorphous form of carbon. It is mainly used as fuel.

  Name a gas used in fire extinguisher.

Ans. Carbon dioxide is used as fire extinguisher.

Which gas is used to produce aerated cold beverages ?

Ans. Carbon dioxide is used to produce aerated cold beverages.

How is hydrocarbon formed?

Ans. Hydrocarbon is formed from the combination of carbon

and hydrogen.

Name the first compound of hydrocarbon.

Ans. The first compound of hydrocarbon is methane.

How many atoms of carbon and hydrogen are present

in the molecule of methane?

Ans. The molecule of methane has one carbon atom and four

hydrogen atoms.

Why is methane called marsh gas ?

Ans. Methane is formed by the decomposition of plants and

animal matter in marshy lands. Hence, methane is called marsh

gas.

(Which gas is formed in a biogas plant ?

Ans. Methane gas is formed in a biogas plant.

Q. 7 Find the odd one out and give the reason :

(1) Anthracite, Charcoal, Bituminous, Peat.

(2) Carbon, Silicon, Sulphur, Phosphorus.

(3) Coke, Diamond, Graphite, Fullerene.

Ans. (1) Charcoal. The others are the types of coal.

(2) Silicon. The others are naturally occurring allotropic elements.

(3) Coke. The others are crystalline allotropes of carbon.

Q. 8 Write whether following statements are True or

False. If a statement is false, correct it and rewrite :

(1) All plant and animal products contain carbon as their main

constituent.

(2) Sulphur is a naturally occurring allotropic element.

(3) The graphite is a non-crystalline form of carbon.

(4) Fullerenes were named after the architect Richard

Buckminster Fuller.

(5) The graphite found in nature is a bad conductor of heat and

electricity.

(6) Charcoal is porous, therefore, it has low density.

(7) Plants make their own food by using oxygen.

(8) Methane is a natural fuel.

(9) Methane has two carbon atoms and four hydrogen atoms.

(10) Carbon dioxide is heavier than air.

Ans. (1) True. (2) True. (3) False. The graphite is a

crystalline form of carbon. (4) True. (5) False. The graphite found

in nature is a good conductor of heat and electricity. (6) True.

(7) False. Plants make their own food by using carbon dioxide.

(8) True. (9) False. Methane has one carbon atom and four

hydrogen atom. (10) True.

Q. 9 Fill in the blanks :

1. (1) In graphite crystal, six carbon atoms form a ……… and are

at specific distances from one another.

* (2) Fullerene is an ……… of carbon.

* (3) ……… turns lime water milky.

* (4) The charcoal is an ……… form of carbon.

* (5) Diamond is ……… conductor of electricity.

* (6) Biogas plant produces ……… gas.

Ans. (1) hexagon (2) allotrope (3) Carbon dioxide (4) amorphous

(5) bad (6) methane.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

2. (1) Graphite is a ……… form of carbon.

(2) ……… is used to extinguish fires.

* (3) ……… is a good conductor of heat and electricity.

(4) ……… are made by subjecting pure carbon to extremely

high pressure and heating it to a very high temperature.

184 NAVNEET GENERAL SCIENCE DIGEST : STANDARD VIII

(5) Charcoal is ……… and therefore it has low density.

(6) Methane burns with a ……… flame.

Ans. (1) crystalline (2) Carbon dioxide (3) Graphite

(4) Synthetic diamonds (5) porous (6) blue.

Q. 10 Choose the correct options and complete the

following statements :

(1) Carbon has atomic number ………

(a) 4 (b) 6 (c) 8 (d) 12

(2) Bituminous coal has ……… per cent of carbon.

(a) 60 (b) 80 (c) 22 (d) 44

(3) ……… is one of the naturally occurring allotropic element.

(a) Magnesium (b) Calcium (c) Phosphorus (d) Silicon

(4) In the diamond crystal, every carbon atom has………atoms

of carbon at specific distances around it.

(a) 3 (b) 5 (c) 6 (d) 4

(5) ……… is a non-crystalline form of carbon.

(a) Graphite (b) Coke (c) Fullerene (d) Diamond

(6) ……… gas is obtained from biogas plant.

(a) Ethane (b) Methane (c) Carbon dioxide (d) Oxygen

(7) The molecular formula of methane is ……… .

(a) C

_

H

_

(b) C

_

H

_

(c) CH

_

(d) C

         

H

_

(8) ……… is produced and it gushes out of fire extinguisher.

(a) Carbon dioxide (b) Methane (c) Oxygen (d) Ethane

Ans. (1) 6 (2) 60 (3) Phosphorus (4) 4 (5) Coke (6) Methane

(7) CH

_

(8) Carbon dioxide.

Q. 11 Match the following :

* [1] ‘A’ ‘B’

(1) Fullerene (a) Na

_

CO

         

(2) Graphite (b) Cutting metals

(3) Diamond (c) Hexagonal arrangements of atoms

(4) Washing soda (d) C

__

Ans. (1) Fullerene –C

__

(2) Graphite – Hexagonal arrangements

of atoms (3) Diamond– Cutting metals (4) Washing

soda –Na

_

CO

         

.

 [2] ‘A’ ‘B’

(1) Methane (a) Amorphous form of carbon

(2) Anthracite (b) Carbon dioxide

(3) Coke (c) Marsh gas

(4) Fire extinguisher (d) 80% carbon

Ans. (1) Methane– Marsh gas (2) Anthracite –80% carbon

(3) Coke – Amorphous form of carbon (4) Fire extinguisher –

Carbon dioxide.