Carbon & Its Compounds

Exercise I

Question 1

Fill in the blanks:

(a) ............... is present in both living and non-living things.

(b) The tendency of an element to exist in two or more forms but in the same physical state is called ............... .

(c) ............... and ............... are the two major crystalline allotropes of carbon.

(d) ............... is the hardest substance that occurs naturally.

(e) The name 'carbon' is derived from the Latin word ............... .

Answer

(a) Carbon

(b) Allotropy

(c) Graphite, Diamond

(d) Diamond

(e) Carbo

Question 2(a)

In combined state, carbon occurs as

1. coal
2. diamond
3. graphite
4. petroleum

Answer

petroleum

Reason — In combined state, carbon occurs in natural gas, petroleum.

Question 2(b)

A crystalline form of carbon is

1. lamp black
2. gas carbon
3. sugar
4. fullerene

Answer

Fullerene

Reason — Fullerene is a crystalline form of carbon.

Question 2(c)

Graphite is not found in

1. Bihar
2. Maharashtra
3. Odisha
4. Rajasthan

Answer

Maharashtra

Reason — In India, graphite is found in Jammu and Kashmir, Bihar, Odisha, Rajasthan and West Bengal.

Question 2(d)

Diamond is used for

1. making the electrodes of electric furnaces.
2. making crucibles for melting metals.
3. cutting and drilling rocks and glass.
4. making carbon brushes for electric motors.

Answer

cutting and drilling rocks and glass

Reason — Diamond is used for cutting and drilling rocks and glass as it is very hard.

Question 2(e)

Carbon forms innumerable compounds because

1. it has four electrons in its outermost shell.
2. it behaves as a metal as well as a non-metal.
3. carbon atoms can form long chains.
4. it combines with other elements to form covalent compounds.

Answer

carbon atoms can form long chains

Reason — Carbon forms innumerable compounds because it has a unique property to link themselves together to form very long chains of different sizes which may be straight, branched or cyclic. This property is called catenation.

Question 3

Write True or False against the following statements:

(a) Carbon constitutes 0.03% of the earth's crust.

(b) Graphite is the purest form of carbon.

(c) Coloured diamonds are costlier than colourless and transparent diamonds.

(d) Graphite has layers of hexagonal carbon bondings.

(e) Diamond is insoluble in all solvents.

Answer

(a) True

(b) False
Correct statement — Diamond is the purest form of carbon.

(c) False
Correct statement — Colourless and transparent diamonds are costlier than coloured diamonds.

(d) True

(e) True

Question 4

Define the following terms:

(a) Allotropy

(b) Carat

(c) Crystal

(d) Catenation

Answer

(a) Allotropy is defined as the phenomenon due to which an element exists in two or more forms in the same physical state with identical chemical properties but with different physical properties.

(b) The weight of a diamond is expressed in terms of carats, where 1 carat = 0.2 g.

(c) A crystal is a homogeneous solid in which particles are arranged in a definite pattern due to which they have a definite geometrical shape with a plane surface.

(d) Carbon atoms possess a unique property to link themselves together to form very long chains of different sizes which may be straight, branched or cyclic and this property is called catenation.

Question 5

State the terms:

(a) Substances whose atoms or molecules are arranged in a definite pattern.

(b) Different forms of an element found in the same physical state.

(c) The property by which atoms of an element link together to form long chain or ring compounds.

Answer

(a) Crystals

(b) Allotropy

(c) Catenation

Question 6

Name the following:

(a) The hardest naturally occurring substance.

(b) A greyish black non-metal that is a good conductor of electricity.

(c) The third crystalline form of carbon.

Answer

(a) Diamond

(b) Graphite

(c) Fullerene

Question 7(a)

Why is graphite a good conductor of electricity but not diamond?

Answer

In a graphite molecule one valence electron of each carbon atom remains free, so it is a good conductor of electricity. But in diamond there is no free or mobile electrons so it does not conduct electricity.

Question 7(b)

Why is diamond very hard?

Answer

In diamond, a carbon atom has four valence electrons. Each carbon atom is linked with four neighbouring carbon atoms forming a rigid tetrahedral structure. Due to this strong bonding diamond is very hard.

Question 7(c)

What are fullerenes? Name the most common fullerene.

Answer

Fullerenes are the third crystalline form of carbon. In fullerenes, many carbon atoms are held together in a cage-like structure. The most common fullerene is buckminster fullerene or buckyball.

Question 7(d)

What impurity is present in black diamond?

Answer

Black diamonds have copper oxide present in them as an impurity.

Question 8

Give two uses of:

(a) graphite

(b) diamond

Answer

(a) The two uses of graphite are:

1. It is used for making the electrodes of electric furnaces.
2. It is used for making lead pencils.

(b) The two uses of diamond are:

1. It is used in jewellery as a gem.
2. Impure diamond is used to cut and drill rocks, glass or other diamonds.

Question 9

Write three differences between graphite and diamond.

Answer

Exercise II

Question 1

Fill in the blanks:

(a) ............... is formed when charcoal is burnt in a limited supply of air.

(b) Coal is a ............... form of carbon.

(c) ............... is the most inferior form of coal.

(d) Wood charcoal is a ............... conductor of heat and electricity.

(e) ............... is used in making black shoe polish.

Answer

(a) Carbon monoxide

(b) amorphous

(c) Peat

(d) bad

(e) Lamp black (soot)

Question 2(a)

Anthracite is

1. an inferior type of coal
2. a superior type of coal
3. a cheapest form of coal
4. none of the above

Answer

a superior type of coal

Reason — Anthracite is the purest variety of coal. Its carbon content is between 92-98%.

Question 2(b)

Destructive distillation of coal yields

1. coal tar
2. coal gas
3. coke
4. all of the above

Answer

All of the above

Reason — Destructive distillation of coal produces coke, coal tar, coal gas and ammoniacal solution.

Question 2(c)

Lamp black is

1. an amorphous form of carbon
2. a crystalline form of carbon
3. a pure form of carbon
4. a cluster of carbon atoms

Answer

an amorphous form of carbon

Reason — Lamp black is an amorphous form of carbon which contains 98-99% carbon.

Question 2(d)

The process by which decayed plants slowly convert into coal is called

1. petrification
2. carbonization
3. carbonification
4. fermentation

Answer

carbonization

Reason — The process by which decayed plants slowly convert into coal is called carbonization.

Question 2(e)

The purest form of the amorphous carbon is

1. wood charcoal
2. sugar charcoal
3. bone charcoal
4. lamp black

Answer

sugar charcoal

Reason — The purest form of the amorphous carbon is sugar charcoal.

Question 3

Write True or False against the following statements.

(a) Charcoal is a good adsorbent.

(b) Coke is obtained by destructive distillation of sugar.

(c) Activated charcoal is a good conductor of electricity.

(d) Wood charcoal is an important constituent of gun powder.

(e) Coal gas is used in the preparation of artificial fertilizers.

Answer

(a) True

(b) False
Correct statement— Coke is obtained by destructive distillation of coal.

(c) False
Correct statement — Activated charcoal is a bad conductor of electricity.

(d) True

(e) False
Correct statement — Ammoniacal solution is used in the preparation of artificial fertilizers.

Question 4

Define the following:

(a) Carbonization

(b) Adsorption

(c) Bone black

Answer

(a) The process of slow conversion of vegetable matter into carbon-rich substances is called carbonization.

(b) Adsorption is the property due to which a substance absorbs gases, liquids and solids only on its surface.

(c) The carbon content of bone charcoal is separated by treating it with hydrochloric acid which dissolves the calcium phosphate. Carbon is filtered out of the solution and in this form it is called bone black or ivory black.

Question 5

Name the following:

1. Substances whose atoms or molecules are not arranged in a geometrical pattern.

2. The best variety of coal.

3. The purest form of amorphous carbon.

4. An amorphous form of carbon that contains about 98% carbon.

5. Mixture of carbon monoxide and hydrogen.

Answer

1. Amorphous substances

2. Anthracite

3. Sugar charcoal

4. Lamp black(soot)

5. Water gas

Question 6(a)

What is destructive distillation? What are the products formed due to the destructive distillation of coal?

Answer

When a substance is heated in the absence of air, the process is called destructive distillation. It results in the decomposition of the substance into its constituent substances. Destructive distillation of coal produces coke, coal tar, coal gas and ammoniacal solution.

Question 6(b)

Why is wood charcoal used in water filters and gas masks?

Answer

Wood charcoal has high adsorbing capacity, so it is used in water filters to remove impurities and in gas masks to adsorb harmful gases.

Question 6(c)

How is wood charcoal made locally? What other substances are formed in the process?

Answer

Locally, wood charcoal is prepared by the following steps:

1. Logs of wood are piled one above the other with a gap in the centre of the pile.
2. The pile is covered with wet clay to prevent the entry of air.
3. A few holes are left at the bottom of the pile.
4. The wood is set on fire.
5. When the fire dies out a greyish-black, brittle, porous solid is left behind which is wood charcoal.

The other substances formed are wood tar, wood gas, pyroligneous acid.

Question 6(d)

How many carbon atoms are there in Buckminster fullerenes?

Answer

60 carbon atoms are there in Buckminster fullerenes.

Question 7(a)

Describe the formation of coal.

Answer

The process of formation of coal is described below:

1. Coal was formed by the bacterial decomposition of ancient vegetable matter buried under successive layers of the earth.
2. Under action of high pressure and temperature, in absence of air, the decayed vegetable matter converted into coal through a series of steps as shown in the figure below.
3. With each successive layer of coal formed, the amount of carbon present in the deposit increased and level of impurities decreased.
4. This process of formation of coal is known as carbonization which took millions of years.

Question 7(b)

Name four types of coal with the percentage of carbon present in each.

Answer

The four types of coal are:

1. Peat — It contains about 50 to 60% carbon.
2. Lignite — It contains more than 60% carbon.
3. Bituminous — There are high, medium and low varieties of bituminous coal with carbon content 90%, 80% and 70-75% respectively.
4. Anthracite — It contains 92-98% carbon content.

Question 8

Name the products formed when:

(a) wood is burnt in the absence of air.

(b) bone is heated in the absence of air.

(c) diamond is burnt in air at 900°C.

(d) graphite is subjected to high pressure and 3000°C temperature.

Answer

(a) Wood charcoal, wood tar, wood gas, pyroligneous acid.

(b) Bone charcoal, bone oil, pyridine.

(c) Carbon dioxide

(d) Artificial diamonds.

Question 9

Give two uses for each of the following:

(a) coal

(b) coke

(c) wood charcoal

(d) sugar charcoal

(e) bone charcoal

(f) lamp black

Answer

(a) Coal

1. It is used both as a domestic and industrial fuel.
2. It is used to prepare coke, coal gas and coal tar.

(b) Coke

1. It is used in the manufacture of water gas (CO + H₂), producer gas (CO + N₂) and artificial graphite.
2. It is used as a smokeless industrial and domestic fuel.

(c) Wood charcoal

1. It is an important constituent of gun powder.
2. Due to its high adsorbing capacity, it is used in military and industrial gas masks to adsorb harmful gases and in water purifier filters.

(d) Sugar charcoal

1. It is used to prepare artificial diamonds.
2. It is used mostly as a reducing agent to extract metals from their respective oxides.

(e) Bone charcoal

1. It is used to decolourise cane sugar in the process of manufacturing sugar.
2. It is used to remove excess of fluoride from water which causes tooth decay.

(f) Lamp black

1. It is used in making black shoe polish, carbon paper, printing ink, black paint etc.
2. It is used in manufacture of tyres and gun powder.

Exercise III

Question 1

(a) Name the chemicals required for the preparation of carbon dioxide in the laboratory.

(b) How will you collect the gas?

(c) Write the balanced chemical equation for the above reaction.

(d) Draw a labelled diagram for the preparation of CO₂ in the laboratory.

(e) Why is sulphuric acid not used for the preparation of carbon dioxide in the laboratory?

Answer

(a) The chemicals required for the preparation of carbon dioxide in the laboratory are:

1. Marble chips (CaCO₃)
2. Dilute hydrochloric acid

(b) The gas is collected by the upward displacement of air.

(c) CaCO₃ + 2HCl ⟶ CaCl₂ + H₂O + CO₂ (g)

(d) Laboratory preparation of carbon dioxide :

(e) Dilute sulphuric acid when reacts with marble chips (CaCO₃) forms calcium sulphate. It is insoluble in water so it covers the marble chips and stops the reaction.

CaCO₃ + H₂SO₄ ⟶ CaSO₄ + H₂O + CO₂ (g)

Question 2

Write the balanced chemical equations for the preparation of carbon dioxide by:

(a) heating calcium carbonate.

(b) the action of acetic acid on sodium bicarbonate.

(c) the action of dilute sulphuric acid on sodium bicarbonate.

(d) the action of dilute hydrochloric acid on sodium carbonate.

Answer

(a) CaCO₃ $\xrightarrow{\enspace\Delta\enspace}$ CaO + CO₂ (g)

(b) NaHCO₃ + CH₃COOH ⟶ CH₃COONa + H₂O + CO₂ (g)

(c) NaHCO₃ + H₂SO₄ ⟶ NaHSO₄ + H₂O + CO₂

(d) Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂

Question 3

What happens when:

(a) a lit splinter is introduced into a jar containing carbon dioxide?

(b) moist blue litmus paper is placed in a jar containing carbon dioxide?

(c) carbon dioxide is passed through lime water first in small amounts and then in excess?

(d) a baking mixture containing baking powder is heated?

(e) a soda water bottle is opened?

Answer

(a) When a lit splinter is introduced into a jar containing carbon dioxide, it extinguishes as carbon dioxide is a non-supporter of combustion.

(b) Carbon dioxide turns moist blue litmus red. This shows that the gas is acidic in nature.

(c) When carbon dioxide is passed through lime water first in small amounts it turns lime water milky. This is due to the formation of insoluble calcium carbonate. When excess of the gas is passed through the solution milkiness disappears. This is due to the formation of a soluble bicarbonate.

(d) When a baking mixture containing baking powder is heated, carbon dioxide gas is formed.

(e) Carbon dioxide gas is dissolved in water under pressure to give soda water. When a soda water bottle is opened, the pressure is released and the bottled gas escapes with a brisk effervescence that adds a fizz to the drink.

Question 4a

Give reasons for the following:

An excess of carbon dioxide increases the temperature of the earth.

Answer

Carbon dioxide gas traps the long wave reflected radiations of sun and keeps our earth warm. But due to air pollution and deforestation excess carbon dioxide gas is emitted and along with other greenhouse gases have created a thermal blanket around the earth, trapping more heat and thus the temperature of the earth increases.

Question 4b

Give reasons for the following:

Soda-acid and foam-type of fire extinguishers are not used for extinguishing electrical fires.

Answer

In both soda-acid and foam-type of fire extinguishers, the solutions are prepared in water which conducts electricity. As a result it might generate an electric shock leading to short circuit and another fire.

Question 4c

Give reasons for the following:

Solid carbon dioxide is used for the refrigeration of food.

Answer

Solid carbon dioxide (dry ice) serves as a coolant and a refrigerant so it is used for the refrigeration of food like fruits, vegetables, meat, etc. which otherwise perish easily.

Question 5

What is a fire extinguisher? What is the substance used in the modern type of fire extinguishers? How is it an improvement over the soda-acid and foam-type fire extinguishers?

Answer

Fire extinguishers are devices in which carbon dioxide is produced in different forms to be used as an extinguishing agent.

Liquid carbon dioxide is the substance used in the modern type of fire extinguishers.

Modern type of fire extinguisher is an improvement over the soda-acid and foam-type fire extinguishers in the following ways:

1. Soda-acid fire extinguishers cannot be used for oil fire as the solution ejected being heavier than oil sinks below oil and does not work whereas modern type of fire extinguishers can be used to put out both oil-fed fires and electrical fires.
2. Both the soda-acid and foam-type fire extinguishers solutions are prepared in water which conducts electricity. It might generate an electric shock leading to short circuit and another fire. But in modern type fire extinguishers, liquid carbon dioxide is used which does not conduct electricity. So, it can be used to put out electrical fires.

Question 6

Explain the term greenhouse effect. What are its benefits? How is it harmful?

Answer

The trapping of the earth's radiated energy by carbon dioxide present in the air so as to keep the earth warm is called the greenhouse effect.

Benefits of greenhouse effect are:

1. In colder regions, this principle is applied to grow plants.
2. It makes the surface of earth warm which provides a suitable environment for survival of living organisms.

Due to deforestation and air pollution, the total amount of carbon dioxide in air has increased. Carbon dioxide gas along with other greenhouse gases have created a thermal blanket around the earth, trapping more heat and increasing the greenhouse effect. This further warming of earth is known as global warming which is harmful. Global warming has serious consequences like:

1. It will cause melting of glaciers and ice in polar regions causing floods.
2. Ecological balance will get disturbed, rainfall patterns will be changed.
3. Pattern of crop cultivation will be changed.
4. Many species of plants and animals will get extinct.

Question 7

What steps should be taken to balance carbon dioxide in the atmosphere?

Answer

The steps taken to balance carbon dioxide in the atmosphere are:

1. Growing more trees and plants.
2. Reducing the consumption of fossil fuels.
3. Using filters in the chimneys of factories and power houses.
4. Using smokeless sources of energy like solar energy, biogas etc.

Question 8

State three ways by which carbon dioxide gas is added into the atmosphere.

Answer

The three ways by which carbon dioxide gas is added into the atmosphere are:

1. Combustion of fuels.
2. Respiration of human beings, animals and plants.
3. By volcanic eruptions.

Exercise IV

Question 1

Fill in the blanks:

(a) ............... is formed when carbon is burnt in a limited supply of air or oxygen.

(b) Carbon monoxide burns in air with a ............... flame to form carbon dioxide.

(c) Carbon monoxide is a product of ............... combustion.

(d) A mixture of 95% oxygen and 5% carbon dioxide is called ...............

(e) Carbon monoxide is used as a ............... in the extraction of pure metals from their corresponding ores.

Answer

(a) Carbon monoxide

(b) pale blue

(c) incomplete

(d) carbogen

(e) reducing agent

Question 2

Match the following:

Answer

Question 3

How is carbon monoxide gas formed?

Answer

Carbon monoxide gas is formed from:

1. Incomplete burning of fuels
2. Exhaust gases of automobiles.

Carbon monoxide is a product of incomplete burning or combustion of carbon and fuels.

2C + O₂ $\xrightarrow{\enspace\Delta\enspace}$ 2CO

Question 4

State the poisonous nature of carbon monoxide.

Answer

1. Carbon monoxide is highly poisonous gas. Air containing 0.5% carbon monoxide by volume if inhaled could result in death.
2. Carbon monoxide combines with haemoglobin present in RBCs of our body to form a stable compound carboxyhaemoglobin.
3. This stable compound does not allow haemoglobin to absorb or carry oxygen, thus our body cells gets deprived of oxygen. This causes paralysis of respiratory organs and results in death due to suffocation.

Question 5

Give two uses of carbon monoxide.

Answer

The two uses of carbon monoxide are:

1. It is used in extraction of metals from their ores.
2. It is used in the production of methanol.

Question 6

Why is carbon monoxide called the silent killer?

Answer

It is very dangerous to sleep in a room where coal or wood is burning and its doors and windows are closed. Owning to the limited supply of air in such a room, carbon monoxide is produced. Since the gas is colourless and has a barely detectable smell, people sleeping in the room do not feel its presence and run the risk of carbon monoxide poisoning. That is why carbon monoxide is also called a silent killer.

Question 7

Explain the reducing action of carbon monoxide.

Answer

Carbon monoxide is a strong reducing agent and it reduces the oxides of moderately or less active metals to their respective metals and itself gets oxidized to carbon dioxide in the process.

CuO + CO $\xrightarrow{\enspace\Delta\enspace}$ Cu + CO₂

Question 8

Write two remedies for carbon monoxide poisoning.

Answer

The two remedies for carbon monoxide poisoning are:

1. The victim should be given artificial respiration with carbogen to restore normal breathing.
2. The victim should be immediately brought out into the open.

Question 9

Complete the reactions and balance them.

(a) CuO + CO ⟶

(b) Fe₂O₃ + CO ⟶

Answer

(a) CuO + CO $\xrightarrow{\enspace\Delta\enspace}$ Cu + CO₂

(b) Fe₂O₃ + 3CO $\xrightarrow{\enspace\Delta\enspace}$ 2Fe + 3CO₂