NCERT Solutions – Chapter 4: Carbon and Its Compounds

🧭 Introduction

Carbon and its compounds form the basis of life on Earth. From simple molecules like carbon dioxide to complex organic compounds like glucose, carbon shows remarkable bonding ability. This chapter helps students understand covalent bonds, hydrocarbons, functional groups, and reactions such as combustion, oxidation, addition, and substitution.

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: ✅ (c) 8 covalent bonds
Each carbon atom forms four covalent bonds (three with hydrogen and one with the other carbon).

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

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

Answer: ✅ (c) ketone
Butanone (CH₃–CO–CH₂–CH₃) contains a carbonyl group (C=O) in the middle carbon atom.

Q3. While cooking, if the bottom of the vessel gets blackened on the outside, it means —

(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
Incomplete combustion produces carbon (soot), which blackens the vessel.

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

Answer:
In CH₃Cl (chloromethane), carbon shares electrons with three hydrogen atoms and one chlorine atom to form four single covalent bonds.
Covalent bonds are formed by mutual sharing of electrons, not by transfer.

Q5. Draw the electron dot structures for —

(a) Ethanoic acid (b) H₂S (c) Propanone (d) F₂

Answer:
(a) CH₃COOH
(b) H–S–H
(c) CH₃–CO–CH₃
(d) F–F
Each molecule shows shared pairs of electrons between atoms.

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

Answer:
A series of organic compounds having the same functional group and general formula, and where successive members differ by –CH₂– group, is called a homologous series.
Example: Alkanes – CH₄, C₂H₆, C₃H₈, etc.

Q7. How can ethanol and ethanoic acid be differentiated based on physical and chemical properties?

Answer:

Property	Ethanol	Ethanoic Acid
Odour	Pleasant (alcohol-like)	Sour (vinegar-like)
Reaction with NaHCO₃	No reaction	Produces CO₂ gas
pH	Neutral	Acidic

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 hydrophobic (tail) and hydrophilic (head) parts. In water, they form micelles trapping oil and dirt.
Micelles do not form in ethanol because it is not polar enough to support the separation of soap molecules.

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

Answer:
They have high calorific value, burn with clean flame, and produce large amounts of heat and energy.

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

Answer:
Hard water contains calcium and magnesium ions that react with soap to form insoluble salts called scum, reducing lathering ability.

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

Answer:
Soap solution is basic in nature.

Red litmus → turns blue
Blue litmus → remains blue

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

Answer:
Hydrogenation is the addition of hydrogen to unsaturated hydrocarbons in the presence of a catalyst (Ni or Pt).
Use: Converts vegetable oils into solid fats (margarine/vanaspati ghee).

Q13. Which of the following hydrocarbons undergo addition reactions:

C₂H₆, C₃H₈, C₂H₂, and CH₄

Answer: ✅ C₂H₂ (ethyne)
Only unsaturated hydrocarbons (double or triple bonds) undergo addition reactions.

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

Answer:
Add bromine water (Br₂ in CCl₄).

Unsaturated hydrocarbons: Decolourise bromine water.
Saturated hydrocarbons: Do not react.

Q15. Explain the mechanism of the cleaning action of soaps.

Answer:
Soap molecules form micelles in water.

The hydrophobic tails trap oil/dirt.
The hydrophilic heads remain in water.
When rinsed, the micelle washes away, cleaning the surface.

🧩 Conclusion

The study of Carbon and Its Compounds helps students understand how carbon forms a vast variety of substances — from fuels and plastics to soaps and alcohols. It also highlights the importance of organic chemistry in daily life and industries.