Carbon and its Compounds: Class 10 Important Questions with Answers

Case-based questions (4 marks each)

(i) Why is the flame yellow and the kadhai black? What should be done? (1) (ii) How is vanaspati made from vegetable oil? Give the reaction type and catalyst. (1) (iii) Name the acid in vinegar, its percentage, and write its reaction with baking soda. (2)

(i) Name A, B and C. (1) (ii) Write the equation for the formation of C and name the reaction. (1) (iii) Write the equation for C + NaOH; name this reaction and state where it is used. (2)

(i) Name the ions that make water hard. (1) (ii) What is the white layer and how does it form? (1) (iii) Why does a detergent work in hard water? Explain how soap removes oily dirt in soft water. (2)

(i) What are P and Q called in relation to each other? (1) (ii) Draw P and Q. (1) (iii) Is R saturated? Write the general formula of its family and the product of its reaction with H₂. (2)

20 MCQs (1 mark each)

1. Number of valence electrons in carbon:
   (a) 2 (b) 4 (c) 6 (d) 8
2. The bond in an N₂ molecule is
   (a) single (b) double (c) triple (d) ionic
3. Covalent bonds in ethene (C₂H₄), counting C=C as one bond:
   (a) 4 (b) 5 (c) 6 (d) 7
4. The allotrope of carbon that conducts electricity:
   (a) diamond (b) graphite (c) C-60 only (d) none
5. General formula of alkynes:
   (a) C_nH_2n+2 (b) C_nH_2n (c) C_nH_2n−2 (d) C_nH_n
6. Which is unsaturated?
   (a) C₃H₈ (b) C₂H₆ (c) C₃H₆ (d) CH₄
7. Successive members of a homologous series differ in mass by
   (a) 12 u (b) 14 u (c) 16 u (d) 18 u
8. Functional group of an aldehyde:
   (a) –OH (b) –CHO (c) –COOH (d) >C=O
9. CH₃COCH₃ is
   (a) propanal (b) propanol (c) propanone (d) propanoic acid
10. Number of structural isomers of pentane:
    (a) 2 (b) 3 (c) 4 (d) 5
11. Formula of benzene:
    (a) C₆H₁₂ (b) C₆H₆ (c) C₆H₁₄ (d) C₅H₁₀
12. Methane + chlorine in sunlight is a/an
    (a) addition (b) substitution (c) oxidation (d) combustion only
13. Catalyst for hydrogenation of oils:
    (a) Fe (b) Ni (c) Pt only (d) V₂O₅
14. Ethanol heated with excess conc. H₂SO₄ at 443 K gives
    (a) ethane (b) ethene (c) ethyne (d) ethanoic acid
15. Gas evolved when sodium reacts with ethanol:
    (a) O₂ (b) CO₂ (c) H₂ (d) no gas
16. Vinegar contains about
    (a) 1–2% (b) 5–8% (c) 20–30% (d) 50% acetic acid
17. Esters are formed from
    (a) acid + base (b) alcohol + acid (c) alcohol + base (d) two alcohols
18. The sweet-smelling product of acetic acid and ethanol is
    (a) ethyl ethanoate (b) sodium acetate (c) ethene (d) methanol
19. Soap solution turns
    (a) blue litmus red (b) red litmus blue (c) both (d) neither
20. In a micelle in water, the hydrocarbon tails point
    (a) outward (b) inward (c) randomly (d) into water

Answer key

Why: 3 → 4 C–H + 1 C=C = 5 bonds (6 shared pairs) · 7 → CH₂ = 12 + 2 = 14 u · 10 → n-, iso-, neo-pentane.

Assertion–Reason (10)

(a) Both A and R true, R explains A · (b) Both true, R does not explain A · (c) A true, R false · (d) A false, R true

1. A: Carbon forms covalent bonds. R: Carbon has four valence electrons and cannot easily gain or lose four. → (a)
2. A: Diamond is a good conductor of electricity. R: Each carbon in diamond is bonded to four other carbons. → (d)
3. A: Graphite conducts electricity. R: Graphite is an allotrope of carbon. → (b)
4. A: Butane and iso-butane are structural isomers. R: They have the same molecular formula but different structures. → (a)
5. A: Ethene decolourises bromine water. R: Ethene is a saturated hydrocarbon. → (c)
6. A: Members of a homologous series have similar chemical properties. R: They have the same functional group. → (a)
7. A: Methane undergoes addition reactions. R: Methane is unreactive in most conditions. → (d) methane does substitution
8. A: Ethanoic acid is called glacial acetic acid. R: It freezes in cold weather as its m.p. is 290 K. → (a)
9. A: Detergents work in hard water. R: Detergents are sodium salts of long-chain carboxylic acids. → (c) that is soap
10. A: Ethyne–oxygen flame is used for welding. R: Ethyne is an unsaturated hydrocarbon. → (b) reason: very high temperature in pure O₂

Give reasons (2 marks each)

1. Carbon compounds have low melting and boiling points.

Strong covalent bonds are inside molecules, but forces between molecules are weak; little energy is needed to separate the molecules. 2

2. Carbon forms a very large number of compounds.

Catenation (strong C–C bonds forming chains, branches, rings) and tetravalency (bonding with four atoms of C, H, O, N, S, Cl…); bonds are strong due to its small size. 2

3. Unsaturated hydrocarbons burn with a sooty flame.

They have a higher proportion of carbon, which does not burn completely in air; unburnt carbon particles glow (yellow) and form soot. 2

4. Alcohol meant for industry is denatured.

To stop its misuse for drinking, poisonous methanol and a blue dye are added; methanol can cause blindness and death. 2

5. Soap solution appears cloudy.

Soap forms micelles which are large enough to scatter light, so the solution looks cloudy (colloid). 2