Exercises
1. Select the proper option and complete the statements
(single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)
a. A carbon atom forms a covalent bond with other atoms. In this bond the two atoms share electrons.
b. All the carbon bonds in a saturated hydrocarbon share electrons.
c. At least one carbon bond in an unsaturated hydrocarbon is double/multiple.
d. Carbon is the essential element in all the organic compounds.
e. The element hydrogen is present in most organic compound.
2. Answer the following questions
a. Why are carbon and its compounds used as fuels?
Answer: They release a large amount of heat energy when combusted due to high calorific value.
b. In which compound forms does carbon occur?
Answer: Carbon occurs as diamond, graphite, fullerene, coal, charcoal, and in organic compounds like hydrocarbons.
c. Write the uses of diamond.
Answer: Used in cutting tools, jewelry, and as abrasives due to its hardness.
3. Explain the difference:
a. Diamond and graphite.
Answer: Diamond is hard, transparent, and an insulator; graphite is soft, opaque, and a conductor due to different structures.
b. Crystalline and non-crystalline forms of carbon.
Answer: Crystalline forms (diamond, graphite) have ordered structure; non-crystalline (coal, charcoal) have disordered structure.
4. Write scientific reasons
a. Graphite is a conductor of electricity.
Reason: It has free electrons due to its layered structure with delocalized electrons.
b. Graphite is not used in ornaments.
Reason: It is soft, opaque, and lacks the luster and hardness required for ornaments.
c. Limewater turns milky when CO₂ is passed through it.
Reason: CO₂ reacts with calcium hydroxide to form insoluble calcium carbonate.
d. Biogas is an eco-friendly fuel.
Reason: It is renewable, produces less pollution, and uses organic waste.
5. Explain the following.
a. Diamond, graphite and fullerenes are crystalline forms of carbon.
They have definite geometric arrangements of carbon atoms.
b. Methane is called marsh gas.
It is produced by decomposition in marshy areas.
c. Petrol, diesel, coal are fossil fuels.
They are formed from decayed organic matter over millions of years.
d. Uses of various allotropes of carbon: use of CO₂ in fire extinguisher.
CO₂ is denser than air, non-combustible, and displaces oxygen, helping extinguish fires.
e. Practical uses of CO₂.
Used in fire extinguishers, refrigeration, carbonated drinks, and photosynthesis.
6. Write two physical properties each.
a. Diamond: Hard, transparent
b. Charcoal: Black, porous
c. Fullerene: Soluble in organic solvents, forms yellow solutions
7. Complete the following Chemical reactions.
- CO₂ + 2H₂O + Heat → CH₄ + 2O₂ (photosynthesis reverse)
- CH₄ + HCl → CH₃Cl + H₂ (substitution reaction)
- Already given: 2NaOH + CO₂ → Na₂CO₃ + H₂O
8. Write answers to the following in detail.
a. What are the different types of coal? What are their uses?
Anthracite (heating), bituminous (steel production), lignite (electricity), peat (gardening).
b. How will you prove experimentally that graphite is good conductor of electricity?
Connect graphite between a battery and bulb in a circuit; bulb lights up.
c. Explain the properties of carbon.
Forms covalent bonds, exists in allotropes, versatile bonding (tetravalency), basis of organic chemistry.
d. Classify carbon.
Crystalline (diamond, graphite, fullerene) and amorphous (coal, charcoal, coke).
9. How will you verify the properties of carbon dioxide?
Test with limewater (turns milky), extinguishes flame, heavier than air (displaces it).