📘 Chapter 4: Carbon and Its Compounds – Class 10 Science Notes

🔷 I. Introduction to Carbon

• Carbon (C) is a versatile element found in all living organisms.
• Atomic Number = 6; Valency = 4 (Tetravalent).
• Forms covalent bonds by sharing electrons with other atoms (non-metals).

🔷 II. Unique Properties of Carbon

1. Tetravalency:
   Carbon forms 4 covalent bonds to become stable.
   e.g., Methane (CH₄): Carbon shares electrons with 4 hydrogen atoms.
2. Catenation:
   Ability to form long chains or rings with other carbon atoms.
   Forms straight, branched, or ring structures.
3. Isomerism:
   Compounds with the same molecular formula but different structures.
   e.g., C₄H₁₀ has two isomers: n-butane and iso-butane.

🔷 III. Types of Covalent Bonds

• Single bond (–): e.g., CH₄
• Double bond (=): e.g., C₂H₄
• Triple bond (≡): e.g., C₂H₂

🔷 IV. Hydrocarbons

Hydrocarbons are compounds made of hydrogen and carbon.

🔷 V. Functional Groups

Group of atoms giving characteristic properties to compounds:

🔷 VI. Homologous Series

• Series of compounds with same functional group and general formula.
• Successive members differ by –CH₂ unit.
• e.g., Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈)

🔷 VII. Nomenclature of Organic Compounds

Steps:

1. Count carbon atoms: Use root word (Meth, Eth, Prop…)
2. Identify functional group: Use suffix (–ol, –al, –one, etc.)
3. Name the compound

Examples:

• CH₄ → Methane
• CH₃CH₂OH → Ethanol
• CH₃COOH → Ethanoic acid

🔷 VIII. Important Carbon Compounds

1. Ethanol (CH₃CH₂OH)

• Common name: Alcohol
• Physical properties:
  • Colorless, volatile
  • Soluble in water
• Uses:
  • Alcoholic beverages, antiseptics, fuels

Reactions:

• Combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat
• Dehydration with conc. H₂SO₄:
  C₂H₅OH → C₂H₄ + H₂O

2. Ethanoic Acid (CH₃COOH)

• Common name: Acetic acid (vinegar = 5-8% solution)
• Sour taste, reacts with bases to form salt + water

Reactions:

• With sodium carbonate:
  2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O
• Esterification (with alcohol):
  CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (pleasant fruity smell)

🔷 IX. Soaps and Detergents

Soaps:

• Sodium or potassium salts of long-chain fatty acids
• Formed by saponification:
  Fat + NaOH → Soap + Glycerol

Micelle formation: Soap molecules form spherical aggregates in water with dirt trapped inside.

Detergents:

• Made from petroleum products
• Work even in hard water

✅ Multiple Choice Questions (MCQs) with Answers

🔹 Conceptual MCQs

1. Carbon is tetravalent because it has:
   a) 4 electrons in its outer shell
   b) 2 electrons in outer shell
   c) 6 valence electrons
   d) 2 valence electrons
   ✅ Answer: a
2. Which of the following is a saturated hydrocarbon?
   a) C₂H₄ b) C₂H₂ c) C₂H₆ d) CH₂
   ✅ Answer: c
3. Which of the following represents a carboxylic acid group?
   a) –OH b) –COOH c) –CHO d) –CO–
   ✅ Answer: b
4. Functional group in ethanol is:
   a) –COOH b) –CHO c) –OH d) –CO–
   ✅ Answer: c

🔹 Application-Based MCQs

5. Which gas is evolved when ethanoic acid reacts with sodium carbonate?
   a) CO₂ b) H₂ c) CH₄ d) O₂
   ✅ Answer: a
6. The compound formed when ethanol is heated with concentrated H₂SO₄ is:
   a) Ethanoic acid b) Methane c) Ethene d) Propane
   ✅ Answer: c
7. Which compound has a pleasant fruity smell?
   a) Ethanol b) Ethanoic acid c) Ester d) Soap
   ✅ Answer: c

🔹 Assertion-Reason MCQs

8. Assertion (A): Detergents work well in hard water.
    Reason (R): They are sodium salts of long-chain fatty acids.
   a) Both A and R are true; R explains A
   b) A is true, R is false
   c) Both A and R are false
   d) A is false, R is true
   ✅ Answer: b
9. Assertion (A): Soaps form scum in hard water.
    Reason (R): Calcium and magnesium ions react with soap.
   ✅ Answer: a

🔹 HOTS MCQs

10. Which of the following is an unsaturated hydrocarbon?
    a) C₂H₆ b) CH₄ c) C₂H₄ d) C₃H₈
    ✅ Answer: c
11. Which of the following is not a property of ethanol?
    a) Volatile b) Soluble in water
    c) Sweet-smelling d) Gives CO₂ on combustion
    ✅ Answer: c
12. What happens when acetic acid reacts with ethanol in the presence of acid?
    a) Soap is formed b) Detergent is formed
    c) Ester is formed d) Alcohol is formed
    ✅ Answer: c