CAIE A-Level Chemistry A2 31.1 Halogen Compounds Questions

Practise preparing halogenoarenes and explaining their lower substitution reactivity than halogenoalkanes.

Exam points

prepare a halogenoarene by arene substitution with Cl2 or Br2 and the matching aluminium halide catalyst
compare warm aqueous AgNO3 results for a halogenoalkane and a halogenoarene such as chlorobenzene
link chlorine lone-pair delocalisation to partial double-bond character, a stronger C–Cl bond and lower reactivity

Covered syllabus points

31.1.1—Preparation of halogenoarenes 31.1.2—Difference in reactivity

[Maximum number: 2]

Describe the difference in reactivity between chloroethane and chlorobenzene with $\mathrm{OH}^{-}(\mathrm{aq})$ .
Explain your answer.

[Maximum number: 3]

Benzene, $\mathrm{C}_{6} \mathrm{H}_{6}$ , is an aromatic molecule.

(a)

Chlorobenzene and chloroethane have different reactivities in nucleophilic substitution reactions.

[ 3 ]

(i)

Identify a suitable reagent to illustrate this difference in reactivity.

The reagent chosen should give visibly different results with chlorobenzene and chloroethane.

[ 1 ]

(aqueous / alkaline) $\mathrm{AgNO}_{3}$ / silver nitrate

(ii)

Write equations to describe any reactions that occur.

[ 1 ]

$\begin{aligned} \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}+\mathrm{HCl} \quad l \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{NaOH} \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}+\mathrm{NaCl} \text { AND } \mathrm{Ag}^{+}+\mathrm{Cl}^{-} \rightarrow \mathrm{AgCl} \text { AND NO equation shown for } \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Cl} \end{aligned}$

(iii)

Explain the difference in the reactivities of chlorobenzene and chloroethane in nucleophilic substitution reactions.

[ 1 ]

[Maximum number: 3]

Organochlorine compounds can undergo hydrolysis.

\mathrm{R}-\mathrm{Cl}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{R}-\mathrm{OH}+\mathrm{HCl}

State and explain the relative rates of hydrolysis of the following compounds.

\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl} \quad \mathrm{CH}_{3} \mathrm{COCl} \quad \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Cl}

M1: $\mathrm{CH}_{3} \mathrm{COCl}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}>\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Cl}$

M2 & M3 any two from:

- in $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Cl}$ (no hydrolysis) C-Cl bond is part of delocalised system OR p-orbital on Cloverlaps with $\pi$ system OR electrons from Cloverlap with $\pi$ system

- $\mathrm{CH}_{3} \mathrm{COCl}$ carbon in C-Cl bond is more electron deficient since it is also attached to an oxygen atom (ora) or C-Cl bond strength is weakest in $\mathrm{CH}_{3} \mathrm{COCl}$ (ora)

- $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}$ carbon in C-Cl bond strengthened by positive inductive effect of alkyl group

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

Question 3