IB DP Chemistry - Reactivity 3.3 Electron sharing reactions - IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Detailed solution
Heterolytic fission breaks a covalent bond unevenly, producing a positive and a negative ion.
For Br–Br: \( \text{Br–Br} \rightarrow \text{Br}^+ + \text{Br}^- \).
✅ Answer: (C) .
▶️ Answer/Explanation
Detailed solution
Chlorine free radical: \( \text{Cl}\cdot \)
- Statement I: A chlorine atom has 17 electrons, not 18 — so this is false.
- Statement II: A free radical is neutral (uncharged), so this is true.
- Statement III: Chlorine radicals form when \( \text{Cl}_2 \) undergoes homolytic fission, so this is true.
Therefore, only statements II and III are correct.
✅ Answer: (C)
▶️ Answer/Explanation
Detailed solution
Free radical substitution occurs when alkanes react with halogens in the presence of UV light. UV light causes homolytic fission of the halogen molecule, forming radicals.
- Option A: Substitution on benzene occurs by electrophilic substitution, not radical substitution.
- Option B: This is hydrogenation of benzene, not a radical reaction.
- Option C: This is electrophilic addition of HBr to an alkene, not a radical mechanism.
- Option D: Reaction of ethane with chlorine under UV light is a classic free radical substitution.
Thus, the reaction that proceeds by a free radical mechanism under UV light is:
\(\boxed{\text{CH}_3\text{CH}_3 + \text{Cl}_2 \rightarrow \text{CH}_3\text{CH}_2\text{Cl} + \text{HCl}}\)
✅ Answer: (D)