Chapter 9 – Carbon and Its Compounds

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Book Name	: Concise Chemistry Middle School
Subject	: Chemistry
Class	: 8
Publisher	: Selina Publisher PVT Ltd
Chapter Name	: Carbon and Its Compounds

EXERCISE- I

Question 1.

Fill in the blanks.

1. ____ is present in both living and non-living things.
2. The tendency of an element to exist in two or more forms but in the same physical state is called ____.
3. ____ and ____ are the two major crystalline allotropes of carbon.
4. ____ is the hardest substance that occurs naturally.
5. The name ‘carbon’ is derived from the Latin word ____.

Answer

1. carbon
2. allotropy
3. graphite, diamond
4. Diamond
5. carbo

Question 2.

Choose the correct alternative.

(a) In a combined state, carbon occurs as

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

(b) A crystalline form of carbon is

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

(c) Graphite is not found in

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

(d) Diamond is used for

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

(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

1. (iv) petroleum
2. (iii) sugar
3. (ii) Maharashtra
4. (iii) cutting and drilling rocks and glass.
5. (iii) carbon atoms can form long chains.

Question 3.

Write ‘true’ or ‘false’ against the following statements.

1. Carbon constitutes 0.03% of the earth’s crust.
2. Graphite is the purest form of carbon.
3. Coloured diamonds are costlier than colourless and transparent diamonds.
4. Graphte has layers of hexagonal carbon bondings.
5. Diamond is insoluble in all solvents.

Answer

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

Question 4.

Define the following terms:

1. Allotropy
2. Carat
3. Crystal
4. Catenation

Answer

1. Allotropy: The existence of an element in two or more physically and chemically different forms is called allotropy.
2. Carat: A unit of measurement used for gemstones, equal to 200 milligrams is called a carat.
3. Crystal: A solid material whose atoms or molecules are arranged in a highly ordered, repeating pattern extending in all three spatial dimensions is called crystal.
4. Catenation: The ability of atoms of an element to form covalent bonds with other atoms of the same element to form long chains or rings is called catenation.

Question 5.

State the terms:

1. Substances whose atoms or molecules are arranged in a definite pattern.
2. Different forms of an element are found in the same physical state.
3. The property by which atoms of an element link together to form long chain or ring compounds.

Answer

1. Crystals.
2. Allotropy.
3. Catenation.

Question 6.

Name the following:

1. The hardest naturally occurring substance.
2. A greyish-black non-metal that is a good conductor of electricity.
3. The third crystalline form of carbon.

Answer

1. Diamond.
2. Graphite.
3. Fullerenes.

Question 7.

Answer the following questions:

Question 7 (a)

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

Answer

One valence electron of each carbon atom remains free in a graphite molecule, thus making graphite a good conductor of electricity. Whereas diamonds have no free mobile electron. That is why diamonds are bad conductors of electricity.

Question 7 (b)

Why is diamond very hard?

Answer

Diamond is very hard because it has a rigid, three-dimensional lattice structure made up of strong covalent bonds between its carbon atoms.

Question 7 (c)

What are fullerenes? Name the most common fullerenes.

Answer

Fullerenes are a class of allotropes of carbon that consist of molecules with a hollow spherical or cylindrical shape, composed entirely of carbon atoms arranged in a pattern of hexagons and pentagons.

Common fullerenes are C-32, C-50, C-70 and C-76

Question 7 (d)

What impurity is present in black diamonds?

Answer

Copper oxide present in black diamonds is an impurity.

Question 7 (e)

Explain the softness of graphite with reference to its structure.

Answer

Graphite is soft because its structure consists of layers of carbon atoms that are loosely held together by weak intermolecular forces. These layers can slide over each other easily, allowing the graphite to be easily scratched or worn away.

Question 8

Give two uses of

1. graphite
2. diamond.

Answer

(a) Two uses of graphite:

1. For making the electrodes of electric furnaces.
2. For making crucibles for melting metals due to their high melting points.

(b) Two uses of diamond:

1. Diamond is used in jewellery as a gem
2. It is used for cutting and drilling rocks, and glass.

Question 9.

Write three differences between graphite and diamond.

Answer

Properties	Diamond	Graphite
Color and opacity	Colorless, transparent	Greyish black, opaque
Texture	Hard	Soft and greasy to touch
Density	High (3.5 g/cm^3)	Low (2.39 g/cm^3)
Electrical conductivity	Bad conductor of electricity	Good conductor of electricity
Combustion temperature	Burns in air at 900°C to form carbon dioxide	Burns in air at 700°C to form carbon dioxide

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Exercise – II

Question 1.

Fill in the blanks:

1. ____ is formed when charcoal is burnt in a limited supply of air.
2. Coal is a ____ form of carbon.
3. ____ is the most inferior form of coal.
4. Wood charcoal is a ____ conductor of heat and electricity.
5. ____ is used in making black shoe polish.

Answer

1. Carbon
2. Amorphous
3. Lignite
4. Bad
5. Carbon black

Question 2.

Choose the correct alternative :

(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

(b) Destructive distillation of coal yields

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

(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

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

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

(e) The purest form of the amorphous carbon is

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

Answer

1. Anthracite is a superior type of coal.
2. Destructive distillation of coal yields all of the above: coal tar, coal gas, and coke.
3. Lamp black is an amorphous form of carbon.
4. The process by which decayed plants slowly convert into coal is called carbonisation.
5. lamp black

Question 3.

Write ‘true’ or ‘false’ against the following statements:

1. Charcoal is a good adsorbent.
2. Coke is obtained by destructive distillation of sugar.
3. Activated charcoal is a good conductor of electricity.
4. Wood charcoal is an important constituent of gun powder.
5. Coal gas is used in the preparation of artificial fertilizers.

Answer

1. True – Charcoal has a highly porous structure that allows it to trap impurities and contaminants in gases, liquids, and solids.
2. False – Coke is obtained by destructive distillation of coal, not sugar.
3. False – Activated charcoal is a poor conductor of electricity due to its low density and high resistance.
4. True – Wood charcoal is one of the three key components of gunpowder, along with saltpeter and sulfur.
5. True – Coal gas is used as a feedstock in the production of ammonia, which is a key component of many artificial fertilizers.

Question 4.

Define the following:

1. Carbonization
2. Adsorption
3. Bone black

Answer

1. Carbonization: The process of converting organic matter into carbon or a carbon-rich residue by heating it in the absence of air is called carbonization.
2. Adsorption: The process by which a substance, usually a solid, accumulates or sticks to the surface of another substance, usually a liquid or gas is called absorption.
3. Bone black: A type of charcoal made from animal bones that are commonly used as a black pigment in inks, paints, and dyes, as well as a filter and decolorizing agent is called bone 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
2. Anthracite
3. Lamp black
4. Carbon black
5. water gas

Answer the following questions :

Question 6 (a)

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

Answer

Destructive distillation is the process of heating an organic substance, such as coal, in the absence of air to break it down into simpler substances. The products formed due to the destructive distillation of coal include coal gas, coal tar, and coke.

Question 6 (b)

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

Answer

Wood charcoal is used in water filters and gas masks because it has a highly porous structure that allows it to trap impurities and contaminants. It is an effective adsorbent due to its high surface area and the presence of small pores and channels that can capture and hold a variety of pollutants, including bacteria, viruses, and harmful gases.

Question 6 (c)

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

Answer

Wood charcoal can be made locally by heating wood in the absence of air. The heat causes the wood to break down into charcoal and other volatile gases and liquids, which are burned off or collected for other uses.

Other substances that may be formed in the process include tar, creosote, and other organic compounds.

Question 6 (d)

How many carbon atoms are there in Buckminster fullerenes?

Answer

Buckminsterfullerene, also known as C – 60, has 60 carbon atoms arranged in a pattern of hexagons and pentagons to form a hollow sphere.

Question 7.

1. Describe the formation of coal,
2. Name four types of coal with the percentage of carbon present in each, with uses.

Answer

(a) Formation of coal: The formation of coal took millions of years. Coal was formed by the bacterial decomposition of ancient vegetable matter hurried under successive layers of the earth. Under in action of high temperatures and pressure, and in the absence of air, the decayed vegetable matter is converted into coal.

(b) Types of Coal:

1. Peat: It is light brown in colour and contains only 50 – 60% carbon. It is the most inferior form of coal.
2. Lignite: it contains more than 60% carbon. It is brown in colour and harder than peat.
3. Bituminous: It has 90%, 80%, and 70 – 75% carbon contents. Bituminous coal is the most common variety of coal and is used as household coal.
4. Anthracite: It is the purest variety of coal. Its carbon contents vary between 92 –98%. It is hard, dense and black, difficult to ignite.

Uses of coal:

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

Question 8.

Name the product formed when:

1. wood is burnt in the absence of air.
2. bone is heated in the absence of air.
3. diamond is burnt in air at 900ºC.
4. graphite is subjected to high pressure and 3000ºC temperature.

Answer

1. Charcoal.
2. Bone char.
3. Carbon dioxide gas.
4. Diamond.

Question 9.

Give two uses for each of the following:

1. coal
2. coke
3. wood charcoal
4. sugar charcoal
5. bone charcoal
6. lampblack

Answer

(a) Uses of coal:

1. Power generation
2. Steel production

(b) Uses of Coke:

1. Fuel for blast furnaces in iron and steel production
2. Production of electrodes for electric arc furnaces

(c) Uses of wood charcoal:

1. Cooking and grilling
2. Water filtration

(d) Uses of sugar charcoal:

1. Production of activated carbon for water and air purification
2. Fuel for small-scale industrial processes

(e) Uses of bone charcoal:

1. Decolorizing and refining sugar syrups and oils
2. Production of black pigment for inks and dyes

(e) Uses of Lampblack:

1. Production of ink and toner
2. Manufacturing of rubber and plastics

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Exercise – III

Question 1.

1. Name the chemicals required for the preparation of carbon dioxide in the laboratory.
2. How will you collect the gas ?
3. Write the balanced chemical equation for the above reaction.
4. Draw a labelled diagram for the preparation of CO2 in the laboratory.
5. Why is sulphuric acid not used for the preparation of carbon dioxide in the laboratory ?

Answer

(a) Calcium carbonate and dilute hydrochloric acid.

(b) By upward displacement of air.

(c) CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.

(d) Laboratory preparation of carbon dioxide

(e) Dilute sulphuric acid reacts with calcium carbonate. But it is not used because the calcium sulphate which is formed during the reaction is insoluble in water. It covers the marble chips and stops the reaction.

H₂SO₄ + CaCO₃ → CaSO₄ + CO₂ + H₂O

Question 2.

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

1. heating calcium carbonate.
2. the action of acetic acid on sodium bicarbonate.
3. the action of dilute sulphuric acid on sodium bicarbonate.

Answer

1. CaCO₃ (s) → CaO (s) + CO₂ (g)
2. NaHCO₃ (s) + CH₃COOH (aq) → CH₃COONa (aq) + CO₂ (g) + H₂O (l)
3. NaHCO₃ (s) + H₂SO₄ (aq) → Na₂SO₄ (aq) + CO₂ (g) + H₂O (l)

Question 3.

What happens when:

1. a lit splinter is introduced into a jar containing carbon dioxide ?
2. moist blue litmus paper is placed in a jar containing carbon dioxide ?
3. carbon dioxide is passed through lime water first in small amounts and then in excess ?
4. a baking mixture containing baking powder is heated?
5. a soda water bottle is opened ?

Answer

1. Lit splinter extinguishes.
2. Blue litmus paper turns red.
3. When CO₂ is passed through lime water in small amounts, it turns milky, when passed in excess milkiness disappears.
4. Carbon dioxide is formed.
5. When the pressure is released the bottled gas escapes with a bristling effervescence that adds fizz to the drink.

Question 4.

Give reasons for the following:

1. An excess of carbon dioxide increases the temperature of the earth.
2. Soda acid and foam types of fire extinguishers are not used for extinguishing electrical fires.
3. Solid carbon dioxide is used for the refrigeration of food.

Answer

1. Excess carbon dioxide increases the temperature of the earth. Due to the rise in temperature ice in the polar regions may melt causing floods in coastal regions island.
2. In both of these fire extinguishers, the solutions are prepared in water, which conducts electricity. As a result, an electric shock might result, which might lead to shortcircuiting and another fire.
3. Solid carbon dioxide serves as a coolant and refrigeration for preserving food articles.

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-type and foam-type fire extinguishers?

Answer

A fire extinguisher is a device used to put out small fires or contain them until professional help arrives. It works by expelling a substance onto the fire that removes one or more of the components necessary for the fire to continue burning.

The substance used in modern fire extinguishers is typically a dry powder, such as mono ammonium phosphate or sodium bicarbonate. This powder works by smothering the fire and preventing it from getting the oxygen it needs to continue burning.

This type of fire extinguisher is an improvement over soda acid-type and foam-type extinguishers because it is more versatile and can be used on a wider range of fires. It is also more effective and leaves less residue, making it easier to clean up after use. Additionally, it can be used from a safer distance and is less likely to cause harm to the user.

Question 6.

Explain the term ‘green house effect’. How can it be both beneficial and harmful for life on earth ?

Answer

Greenhouse effect— 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’. The greenhouse is beneficial because this principle is applied to grow plants in colder regions.

Carbon dioxide increases the temperature of the atmosphere. Due to rise in temperature; ice in the polar regions may melt, causing floods. So it is harmful to life on Earth.

Question 7.

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

Answer

As global warming will cause an unbalanced ecological system, serious efforts should be made to balance the percentage of carbon dioxide in the atmosphere. Some of these steps are:

• Growing more trees and plants.
• Using smokeless sources of energy like solar energy, biogas, etc.
• Using filters in the chimneys of factories and power houses.

Question 8.

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

Answer

1. Carbon dioxide is emitted into the atmosphere through burning fossil fuels for electricity, transportation, and industrial processes.
2. Deforestation causes carbon stored in trees to be released back into the atmosphere.
3. Various industrial processes, such as cement production and chemical manufacturing, also release carbon dioxide into the atmosphere as a byproduct.

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Exercise – IV

Question 1.

Fill in the blanks:

1. ____ is formed when carbon is burnt in a limited supply of air or oxygen.
2. Carbon monoxide bums in the air with a ____ flame to form carbon dioxide.
3. Carbon monoxide is a product of ____ combustion.
4. A mixture of 95% oxygen and 5% carbon dioxide is called ____.
5. Carbon dioxide is used as a ____ agent in the extraction of pure metals from their corresponding ores.

Answer

1. Carbon monoxide
2. pale blue
3. incomplete
4. carbogen
5. reducing

Question 2.

Match the following

Column A	Column B
1. A product of incomplete burning	(a) Hopcolite
2. Nature of carbon monoxide	(b) Combustible gas
3. A compound formed by the combination of haemoglobin and carbon monoxide	(c) Carboxy-haemoglobin
4. A mixture of metallic oxides	(d) Carbon monoxide
5. Carbon monoxide	(e) Highly poisonous

Answer

Column A	Column B
1. A product of incomplete burning	(d) Carbon monoxide
2. Nature of carbon monoxide	(e) Highly poisonous
3. A compound formed by the combination of haemoglobin and carbon monoxide	(c) Carboxy-haemoglobin
4. A mixture of metallic oxides	(a) Hopcolite
5. Carbon monoxide	(b) Combustible gas

Question 3.

How is carbon monoxide gas formed?

Answer

Mostly carbon monoxide is formed when a large amount of carbon or its compounds is burnt in a limited supply of air or oxygen.

2C (s) + O₂ (g) → 2CO (g)

Question 4.

State the poisonous nature of carbon monoxide?

Answer

Carbon monoxide is a highly poisonous gas that is colorless, odorless, and tasteless. It is poisonous because it binds to hemoglobin in the blood, reducing its ability to carry oxygen to the body’s tissues. This can lead to a range of health effects, from headaches, dizziness, and nausea to unconsciousness and even death in severe cases.

Question 5.

Give two uses of carbon monoxide.

Answer

Uses of carbon monoxide:

1. Carbon monoxide is a strong reducing agent.
2. Carbon monoxide is used in the extraction of pure metals from their ores.

Question 6.

Why is carbon monoxide called silent killer ?

Answer

Carbon monoxide is produced by burning coal or wood in a limited supply of air. Since the gas is colourless and a barely detectable smell, people do not feel it and it can be proven as a silent killer.

Question 7.

Explain the reducing action of carbon monoxide.

Answer

Reducing action of carbon- monoxide: Carbon monoxide is a strong reducing agent. It reduces the oxides of the less active metals to their respective metals and itself gets oxidised to carbon dioxide.

3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂

Question 8.

Write two remedies for carbon monoxide poisoning.

Answer

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

Question 9.

Complete the reactions and balance them.

1. CuO + CO →
2. Fe₂O₃ + CO →

Answer

1. CuO + CO → Cu + CO₂
2. Fe₂O₃ + 3CO → 2Fe + 3CO₂