Worksheet: Test Haloalkane and Haloarenes

 

Worksheet: Test Haloalkane and Haloarenes 

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🔹 1-Mark Questions

1. Write the general formula of haloalkanes.
2. Which compound is known as freon-12?
3. Give the IUPAC name of CH₃CH₂CH₂Cl.
4. Write one use of chlorofluorocarbons (CFCs).
5. Name the reagent used in the preparation of alkyl bromide from alcohols.
6. Which haloalkane is used as a local anaesthetic?
7. Write the IUPAC name of C₆H₅Cl.
8. Which catalyst is used in the chlorination of benzene?

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🔹 2-Mark Questions

1. Write one difference between haloalkanes and haloarenes.
2. Explain why alkyl halides are polar in nature.
3. Give the mechanism of the chlorination of methane.
4. Write the equation for the preparation of chloroform from ethanol.
5. Explain the role of anhydrous AlCl₃ in the preparation of haloarenes.
6. How will you prepare ethyl bromide from ethanol? Write the reaction.
7. What happens when benzene reacts with chlorine in presence of sunlight?
8. Write the chemical equation for the preparation of iodoform from ethanol.

Answers to the 1-mark and 2-mark questions from Haloalkanes and Haloarenes:

🔹 1-Mark Questions with Answers

Q1. Write the general formula of haloalkanes.

Ans. General formula: CₙH₂ₙ₊₁X (where X = F, Cl, Br, I).

Q2. Which compound is known as freon-12?

Ans. CCl₂F₂ (Dichlorodifluoromethane).

Q3. Give the IUPAC name of CH₃CH₂CH₂Cl.

Ans. 1-Chloropropane.

Q4. Write one use of chlorofluorocarbons (CFCs).

Ans. Used as refrigerants and propellants.

Q5. Name the reagent used in the preparation of alkyl bromide from alcohols.

Ans. HBr (or mixture of NaBr + H₂SO₄).

Q6. Which haloalkane is used as a local anaesthetic?

Ans. Chloroform (CHCl₃).

Q7. Write the IUPAC name of C₆H₅Cl.

Ans. Chlorobenzene.

Q8. Which catalyst is used in the chlorination of benzene?

Ans. Anhydrous AlCl₃ (Lewis acid).

🔹 2-Mark Questions with Answers

Q1. Write one difference between haloalkanes and haloarenes.

Ans.

Haloalkanes: Halogen atom attached to an sp³ hybridised carbon.

Haloarenes: Halogen atom attached to an sp² hybridised carbon of benzene ring.

Q2. Explain why alkyl halides are polar in nature.

Ans. Due to the electronegativity difference between C (2.5) and halogen (Cl = 3.0, Br = 2.8, I = 2.5, F = 4.0), the C–X bond is polarized, making alkyl halides polar.

Q3. Give the mechanism of the chlorination of methane.

Ans. Free radical substitution:

Initiation: Cl₂ → 2Cl• (UV light).

Propagation: CH₄ + Cl• → CH₃• + HCl;

CH₃• + Cl₂ → CH₃Cl + Cl•.

Termination: Combination of radicals.

Q4. Write the equation for the preparation of chloroform from ethanol.

Ans.

C₂H₅OH → (oxidation) → CH₃CHO

CH₃CHO + 3Cl₂ → CCl₃CHO + 3HCl

CCl₃CHO + NaOH → CHCl₃ + HCOONa

Q5. Explain the role of anhydrous AlCl₃ in the preparation of haloarenes.

Ans. AlCl₃ acts as a Lewis acid catalyst. It polarises the halogen molecule (Cl₂ → Cl⁺ + Cl⁻) and generates the electrophile (Cl⁺), which attacks benzene in electrophilic substitution.

Q6. How will you prepare ethyl bromide from ethanol? Write the reaction.

Ans.

C₂H₅OH + HBr → C₂H₅Br + H₂O

Q7. What happens when benzene reacts with chlorine in presence of sunlight?

Ans. Side-chain substitution does not occur as benzene has no side chain; instead, addition occurs:

C₆H₆ + 3Cl₂ → C₆H₆Cl₆ (Benzene hexachloride, BHC).

Q8. Write the chemical equation for the preparation of iodoform from ethanol.

Ans.

CH₃CH₂OH + I₂ + NaOH → CHI₃ (yellow ppt.) + HCOONa + H₂O