More practice questions

4. Q4. Write the molecular formula of the cycloalkane with six carbon atoms and of the alkyne with six carbon atoms.

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   Cyclohexane, C₆H₁₂ (C_nH_2n); hexyne, C₆H₁₀ (C_nH_2n−2).

5. Q5. How are petrol, diesel and kerosene obtained, and how is coal gas obtained?

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   Petrol, diesel and kerosene by the fractional distillation of petroleum; coal gas by the destructive distillation of coal (NCERT page 295).

6. Q6. Find the degree of unsaturation of naphthalene, C₁₀H₈, and explain it.

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   (20 + 2 − 8)/2 = 7: two fused rings and five C=C bonds in its usual structure.

7. Q7. Name three polymers made from hydrocarbons.

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   Polythene, polypropene and polystyrene (NCERT page 295).

8. Q8. A hydrocarbon has the formula C₅H₁₀ and does not decolourise bromine water (it has no multiple bond). What kind of compound is it?

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   Its degree of unsaturation is (10 + 2 − 10)/2 = 1. With no π bond, the one unsaturation must be a ring: it is a cycloalkane, such as cyclopentane or methylcyclobutane.