CAIE A-Level Chemistry 15.1.7 Rates of Halogenoalkane Hydrolysis

Practise comparing halogenoalkane hydrolysis rates from C–X bond strength and silver-halide precipitate timing.

Exam points

rank C–I as weakest and fastest to hydrolyse, followed by C–Br and then stronger C–Cl
use the time taken for AgI, AgBr or AgCl precipitate to appear as an experimental rate measure
explain a slower chloroalkane than bromoalkane by the greater energy required to break C–Cl

[Maximum number: 2]

Halogenoalkanes react with a number of different reagents in nucleophilic substitution reactions.

Equal amounts of three different halogenoalkanes are added to three separate test-tubes. An equal amount of aqueous silver nitrate and ethanol is added to each test-tube. The time taken for a precipitate to form is recorded for each halogenoalkane.

Table for Question 15.1.7—Rate of hydrolysis of halogenoalkanes question 1 — CAIE A-Level Chemistry AS

Describe and explain the trend in reactivity of the different halogenoalkanes shown in this experiment.

M1 Increasing reactivity from $\mathrm{Cl} \rightarrow \mathrm{Br} \rightarrow \mathrm{I}$

M2 Due to decreasing strength of C-X bond (from C-Cl to C-Br to C-I )

OR

Less energy needed to break C-X (from C-Cl to C-Br to C-I )

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15.1.7—Rate of hydrolysis of halogenoalkanes question 1