Class 10th Science Chapter 4 – Carbon and Its Compounds – Exercises

Q1. Ethane, with the molecular formula C₂H₆ has

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

Answer: (b) 7 covalent bonds

Explanation:

Structure of ethane (C₂H₆):

$$C{H}_3-C{H}_3$$

• C–C bond → 1 covalent bond

• Each carbon forms 3 C–H bonds, so 3 + 3 = 6 covalent bonds

Total covalent bonds = 1 + 6 = 7

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Q2. Butanone is a four-carbon compound with the functional group

(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol

Answer: (c) ketone

Explanation:

• Butanone (C₄H₈O) has the structure:

$$C{H}_3-CO-C{H}_2-C{H}_3$$

• Contains the CO (carbonyl) group in the middle, which is a ketone functional group.

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Q3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

(a) the food is not cooked completely
(b) the fuel is not burning completely
(c) the fuel is wet
(d) the fuel is burning completely

Answer: (b) the fuel is not burning completely

Explanation:

Incomplete burning of fuel produces soot (carbon particles).
This soot deposits as a black layer on the vessel’s bottom.

Q4. Explain the nature of the covalent bond using the bond formation in CH₃Cl.

Answer:

CH₃Cl (chloromethane) is formed by covalent bonding, in which atoms share electrons to achieve stable electronic configuration.

Bond Formation Explanation:

• Carbon (C) has 4 valence electrons → needs 4 more to complete its octet.

• Hydrogen (H) has 1 valence electron → needs 1 more.

• Chlorine (Cl) has 7 valence electrons → needs 1 more.

Sharing of electrons:

• Carbon shares one electron each with three hydrogen atoms → forms three C–H single covalent bonds.

• Carbon shares one electron with chlorine → forms one C–Cl single covalent bond.

• All atoms achieve stable octet/duplet configuration.

Electron dot (Lewis) structure:

$$H:C:H$$

(with Cl attached forming shared pair)

Detailed representation:

$$\begin{array}{c}H\\ \mathrm{\mid }\\ H-C-Cl\\ \mathrm{\mid }\\ H\end{array}$$

Nature of bonds: All bonds (C–H and C–Cl) are covalent because they are formed by sharing of electrons, not by electron transfer.

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Q5. Draw the electron dot structures for:

(a) Ethanoic acid (CH₃COOH)

(b) Hydrogen sulphide (H₂S)

S has 6 valence electrons and forms two single covalent bonds with two H atoms.

$$H:S:H$$

(two lone pairs left on S)

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(c) Propanone (C₃H₆O)

Structure:

$$C{H}_3-CO-C{H}_3$$

Electron dot structure overview:

 

(O joins central carbon using double bond)

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(d) Fluorine (F₂)

Each fluorine atom has 7 valence electrons and shares 1 pair forming a single covalent bond.

$$:F\text{—}F:$$

(Each F has 3 lone pairs outside the shared pair)

Q6. What is a homologous series? Explain with an example.

Answer:

A homologous series is a series of organic compounds having the same functional group and similar chemical properties, in which the molecular formula of each successive member differs by –CH₂– (14 u).

Example: Alkanes

All have the functional group — single covalent bonds (C–C, C–H), and differ by CH₂.

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Q7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Answer:

$$C{H}_{3}COOH+NaHC{O}_3\to C{H}_{3}COONa+H_{2}O+C{O}_2\uparrow$$

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Q8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Answer:

Soap molecules have two ends:

• Hydrophobic tail (repels water, attracts dirt/oil)

• Hydrophilic head (attracts water)

When soap is added to water, hydrophobic ends surround the dirt and hydrophilic ends remain in water, forming micelles.

Micelle diagram explanation:

Dirt is trapped inside a spherical micelle.

Micelles in ethanol?

No micelles will not form in ethanol because ethanol is not polar enough.
Micelle formation requires polar water molecules to keep hydrophilic ends outward.

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Q9. Why are carbon and its compounds used as fuels for most applications?

Answer:

Carbon and its compounds are used as fuels because:

• They have high calorific value (release large amount of heat on burning)

• Their combustion is controlled and clean

• They produce fewer pollutants when burnt completely

Example:

$$C{H}_4+2O_2\to C{O}_2+2H_{2}O+\text{heat}$$

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Q10. Explain the formation of scum when hard water is treated with soap.

Answer:

Hard water contains calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
Soap reacts with these ions to form insoluble salts called scum.

$$2C_{17}{H}_{35}COONa+C{a}^{2+}\to (C_{17}{H}_{35}COO{)}_{2}Ca+2N{a}^{+}$$

Scum wastes soap and prevents lather formation.

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Q11. What change will you observe if you test soap with litmus paper (red and blue)?

Answer:

Soap solution is basic in nature.

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Q12. What is hydrogenation? What is its industrial application?

Answer:

Hydrogenation is a process in which hydrogen is added to unsaturated compounds in the presence of a palladium, nickel or platinum catalyst.

Example:

$$C_2{H}_4+H_2\stackrel{Ni}{\to }{C}_2{H}_6$$

Industrial application:

Used for converting vegetable oils into solid fats like margarine / vanaspati ghee.

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Q13. Which of the following hydrocarbons undergo addition reactions:

C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄?

Answer:

Unsaturated hydrocarbons undergo addition reaction.
Unsaturated compounds contain double or triple bonds.

Correct answer:

$$C_3{H}_6\text{(propene)},C_2{H}_2\text{(ethyne)}$$

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Q14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.

Answer:

Bromine water test

Experiment:

Add bromine water (orange) to the sample.

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Q15. Explain the mechanism of cleaning action of soaps.

Answer:

Soap molecules contain:

• Hydrophobic tail (binds with grease and dirt)

• Hydrophilic head (binds with water)

Steps:

1. Hydrophobic tails attach to oil/dirt particles.

2. Hydrophilic heads stay in water.

3. Micelles are formed trapping dirt inside.

4. Agitation lifts micelles away and washes them off.

Diagram:

(Dirt particle in the centre surrounded by soap molecules in a spherical micelle)