NIOS Class 12 Chemistry Chapter 24 Hydrocarbons

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NIOS Class 12 Chemistry Chapter 24 Hydrocarbons

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Hydrocarbons

Chapter: 24

Module – VII: Chemistry of Organic Compounds

INTEXT QUESTIONS 24.1

1. List four important uses of hydrocarbons.

Ans: They are used as fuels and to prepare detergents, dyes, drugs, explosives etc. Hydrocarbons are used to prepare some important organic compounds like alcohols, aldehydes, carboxylic acids etc.

2. What is Grignard’s reagent in a molecule?

Ans: The alkyl magnesium halides (R-MgX) are called Grignard’s reagent.

3. What is an active hydrogen in a molecule?

Ans: Easily replaceable hydrogen present in a molecule is called active hydrogen.

4. What makes the physical properties of various hydrocarbons different?

Ans: The physical properties of hydrocarbons differ from one another due to difference in molecular mass, surface area, intermolecular force of attraction.

5. Name two alkanes which are gases and two alkanes which are liquids at room temperature.

Ans: Methane and ethane are gases, pentane and hexane are liquids.

6. Name three isomers of pentane.

Ans: Three isomers of pentane are : n-pentane, isopentane and neopentane.

7. Which one has higher b.p. n-butane or n-pentane? Explain.

Ans: n-pentane has higher boiling point than n-butane.

8. Write the balanced chemical equation for the complete combustion of propane.

Ans: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

INTEXT QUESTIONS 24.2

1. Which one has higher boiling point: cis but-2-ene or trans but-2-ene?

Ans: Trans-2-butene has higher boiling point than cis-isomer.

2. Name the products formed when ethene is oxidized with cold alkaline solution of KMnO₄.

Ans: Ethane-1, 2-diol.

3. Write the conditions for hydrogenation of alkenes.

Ans: Hydrogen in presence of catalyst Ni, Pt or Pd.

4. What happens when ethene reacts with oxygen at 575 K in presence of Ag?

Ans: Epoxyethane is produced.

INTEXT QUESTIONS 24.3

1. How is ethyne prepared from calcium carbide?

Ans: Calcium carbide is reacted with water to prepare ethyne.

CaC₂ + 2H₂O 

C₂H₂ + Ca(OH)₂

2. Give one reaction to confirm the acidic nature of ethyne.

Ans: Reaction with sodium metal confirms the acidic nature of ethyne.

H — C ≡ C — H + 2Na 

Na — C ≡ C — Na + H₂

Ethyne Disodium acetylide

3. What is the percentage of s-character in ethane, ethene and ethyne?

Ans: The s-character in : Ethane = 25%,

Ethene = 33%,

Ethyne = 50%

INTEXT QUESTIONS 24.4

1. What is the value of resonance energy of benzene?

Ans: The resonance energy of benzene is 150.3 KJ mol⁻¹.

2. Name the product formed when :

(i) benzene reacts with chlorine in the presence of light.

Ans: Benzene hexachloride (BHC).

(ii) phenol reacts with chlorine in the presence of FeCl₃.

Ans: o-Chlorophenol and p-chlorophenol.

(iii) nitrobenzene reacts with chlorine in the presence of FeCl₃.

Ans: m-Chloronitrobenzene.

3. Classify the following into o-and p- or m-directing groups:

Ans: