Short Introduction

Carbon is one of the most important elements in nature. It forms millions of compounds due to its tetravalency and catenation properties. This chapter explains covalent bonding, hydrocarbons, functional groups, ethanol, ethanoic acid, soaps, detergents, and the versatile nature of carbon. These NCERT Exercise Solutions provide detailed step-by-step answers for better understanding and exam preparation.

Quick Information Box

Particular	Details
Chapter Name	Carbon and Its Compounds
Class	10
Subject	Science
Board	CBSE/NCERT
Chapter Number	4
Main Topics	Covalent Bonding, Hydrocarbons, Functional Groups, Ethanol, Ethanoic Acid, Soaps & Detergents

Concepts Used (Topics Covered)

• Covalent Bond Formation
• Tetravalency of Carbon
• Catenation
• Saturated and Unsaturated Hydrocarbons
• Homologous Series
• Functional Groups
• Ethanol and Ethanoic Acid
• Hydrogenation
• Soap and Detergent Action
• Micelle Formation

Important Formulas

1. Ethane = C₂H₆
2. Ethene = C₂H₄
3. Ethyne = C₂H₂
4. Ethanol = C₂H₅OH
5. Ethanoic Acid = CH₃COOH
6. Hydrogenation:
   Unsaturated Hydrocarbon + H₂ → Saturated Hydrocarbon
7. Neutralization:
   CH₃COOH + NaOH → CH₃COONa + H₂O

NCERT Exercise Questions & Step-by-Step Solutions

Question 1

Ethane (C₂H₆) has:

(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds

Solution

Structure of Ethane:

H₃C—CH₃

Bonds:

• 6 C-H bonds
• 1 C-C bond

Total = 7 covalent bonds

Answer

(b) 7 covalent bonds

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Question 2

Butanone is a four-carbon compound with the functional group:

Solution

The suffix “one” indicates a ketone functional group.

Answer

(c) Ketone

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Question 3

Blackening of vessel bottom indicates:

Solution

Black soot forms due to incomplete combustion of fuel.

Answer

(b) The fuel is not burning completely

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Question 4

Explain the nature of covalent bond using CH₃Cl.

Solution

• Carbon shares four electrons.
• Three electrons are shared with hydrogen atoms.
• One electron is shared with chlorine atom.
• Shared electrons form covalent bonds.

Thus:

• 3 C-H covalent bonds
• 1 C-Cl covalent bond

CH₃Cl is formed by sharing of electrons, hence it contains covalent bonds.

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Question 5(a)

Draw electron dot structure of ethanoic acid.

Solution

H₃C—C(=O)—OH

Carbon shares electrons with oxygen and hydrogen atoms to complete octet.

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Question 5(b)

Draw electron dot structure of H₂S.

Solution

H : S : H

Sulphur shares one electron each with two hydrogen atoms.

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Question 5(c)

Draw electron dot structure of propanone.

Solution

CH₃—CO—CH₃

The oxygen atom forms a double bond with the central carbon atom.

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Question 5(d)

Draw electron dot structure of F₂.

Solution

—F:

Each fluorine atom shares one electron pair.

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Question 6

What is a homologous series?

Solution

A series of organic compounds having:

• Same functional group
• Similar chemical properties
• Successive members differing by CH₂ unit

Example

Methane → CH₄
Ethane → C₂H₆
Propane → C₃H₈

Difference between successive members = CH₂

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Question 7

Differentiate between ethanol and ethanoic acid.

Solution

Property	Ethanol	Ethanoic Acid
Smell	Pleasant	Vinegar smell
Litmus Test	No change	Turns blue litmus red
Reaction with NaHCO₃	No reaction	Produces CO₂ gas
Nature	Neutral	Acidic

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Question 8

Why does micelle formation take place?

Solution

Soap molecules have:

• Hydrophilic head
• Hydrophobic tail

The tails trap oil and grease while heads remain in water. Thus micelles are formed.

Micelles are not formed in ethanol because soap dissolves completely in ethanol.

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Question 9

Why are carbon compounds used as fuels?

Solution

Carbon compounds:

• Burn easily
• Produce large amount of heat
• Have high calorific value
• Are readily available

Hence they are widely used as fuels.

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Question 10

Explain scum formation.

Solution

Hard water contains calcium and magnesium salts.

These react with soap:

Soap + Ca²⁺/Mg²⁺ → Insoluble precipitate

The insoluble precipitate is called scum.

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Question 11

What change is observed with litmus paper?

Solution

Soap solution is basic.

• Red litmus turns blue.
• Blue litmus remains blue.

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Question 12

What is hydrogenation? Give industrial application.

Solution

Hydrogenation is the addition of hydrogen to unsaturated compounds in presence of nickel catalyst.

Example:

Vegetable Oil + H₂ → Vanaspati Ghee

Industrial Application

Manufacture of vanaspati ghee from vegetable oils.

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Question 13

Which hydrocarbons undergo addition reactions?

Given:
C₂H₆, C₃H₈, C₃H₆, C₂H₂, CH₄

Solution

Addition reactions occur in unsaturated hydrocarbons.

Unsaturated compounds:

• C₃H₆ (alkene)
• C₂H₂ (alkyne)

Answer

C₃H₆ and C₂H₂

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Question 14

Differentiate between saturated and unsaturated hydrocarbons.

Solution

Add bromine water.

Observation:

• Unsaturated hydrocarbons decolourize bromine water.
• Saturated hydrocarbons do not.

This test differentiates them.

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Question 15

Explain cleaning action of soap.

Solution

Step 1:
Soap molecules contain hydrophilic heads and hydrophobic tails.

Step 2:
Hydrophobic tails surround grease and dirt.

Step 3:
Micelles are formed.

Step 4:
Dirt gets trapped inside micelles.

Step 5:
During washing, dirt is removed along with water.

Hence soap cleans clothes effectively.

Common Mistakes

1. Confusing ketone with aldehyde.
2. Forgetting CH₂ difference in homologous series.
3. Writing ethanol as acidic.
4. Assuming soap works equally well in hard water.
5. Ignoring the role of catalyst in hydrogenation.

Exam Tips

• Learn all functional groups carefully.
• Remember definitions of catenation and tetravalency.
• Practice electron-dot structures.
• Revise reactions of ethanol and ethanoic acid.
• Frequently asked question: Micelle formation and cleaning action of soap.

Practice MCQs

1. Carbon forms four covalent bonds because of:

A. Monovalency
B. Divalency
C. Trivalency
D. Tetravalency

Answer: D

2. Vinegar contains:

A. Methanoic acid
B. Ethanoic acid
C. Sulphuric acid
D. Hydrochloric acid

Answer: B

3. Functional group of alcohol is:

A. -CHO
B. -COOH
C. -OH
D. >C=O

Answer: C

4. Soap molecules form:

A. Crystals
B. Micelles
C. Salts
D. Gases

Answer: B

5. Unsaturated hydrocarbons contain:

A. Single bond only
B. Double/Triple bond
C. Ionic bond
D. Metallic bond

Answer: B

FAQ Section

Q1. Why is carbon called a versatile element?

Because it shows tetravalency and catenation, forming millions of compounds.

Q2. What is catenation?

The ability of carbon atoms to form long chains with one another.

Q3. What is the functional group of ethanol?

Hydroxyl group (-OH).

Q4. Why does soap not work well in hard water?

Soap forms insoluble scum with calcium and magnesium ions.

Q5. What is the common name of ethanoic acid?

Acetic acid.

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