Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

The reaction in which 1-chloro-1-phenylethane reacts with hydroxide ions to form 1-phenylethanol is: $\text{C}_6\text{H}_5\text{CHClCH}_3 + \text{OH}^- \rightarrow \text{C}_6\text{H}_5\text{CH(OH)CH}_3 + \text{Cl}^-$. The speed of this reaction may be investigated by finding how much hydroxide ion is still present in solution at a chosen time. The reaction can be effectively halted by diluting the solution with an ice-cold solvent.
(a)[4]

Describe a suitable way to investigate the rate of this reaction at $40^\circ\text{C}$, using the following: • a $0.10\ \text{mol dm}^{-3}$ solution of 1-chloro-1-phenylethane, labelled $A$ • a $0.10\ \text{mol dm}^{-3}$ sodium hydroxide solution, labelled $B$ • $0.10\ \text{mol dm}^{-3}$ $\text{HCl}$ • volumetric glassware • ice-cold solvent • stopclock • access to standard laboratory equipment and chemicals

(b(i))[2]

Deduce the order of reaction with respect to each of $[\text{C}_6\text{H}_5\text{CHClCH}_3]$ and $[\text{OH}^-]$. Give your explanation.

(b(ii))[1]

Write the rate equation for this reaction, and state the units of the rate constant, $k$.

(b(iii))[1]

Calculate the relative rate for experiment $4$.

(c(i))[3]

Use your answers in (b)(i) to help you draw the mechanism for the reaction of 1-chloro-1-phenylethane with hydroxide ions, including the following: • every relevant lone pair and dipole • curly arrows to show the movement of electron pairs • the structures of any transition state or intermediate

(c(ii))[1]

This reaction was carried out using a single optical isomer of 1-chloro-1-phenylethane. Use your mechanism in (i) to predict whether the product will be a single optical isomer or a mixture of two optical isomers. Explain your answer.

(d)[4]

A proton NMR spectrum of a sample of 1-phenylethanol has four peaks: a multiplet for the $\text{C}_6\text{H}_5$ protons and three further peaks as listed in the table. After the sample is shaken with $\text{D}_2\text{O}$ and the proton NMR spectrum is measured again, fewer peaks are observed. Complete the table for the proton NMR spectrum of 1-phenylethanol, $\text{C}_6\text{H}_5\text{CH(OH)CH}_3$. You may find the Data Booklet helpful.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: Any correct kinetic method described is acceptable (max 4 marks)

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