Chemistry 9701 · AS & A Level · Halogen compounds

Halogen compounds — practice question

An excess amount of 2-bromo-2-methylpropane is mixed with $0.0010\,\text{mol}$ of $\text{NaOH}(aq)$, together with a few drops of phenolphthalein indicator. As soon as mixing begins, a stopwatch is started. The interval for the pink colour to vanish is then noted. The test is carried out again at other temperatures, while the concentrations and volumes of all reagents are kept the same.
(a)[1]

Explain what is meant by the term rate of reaction.

(b(i))[1]

Mark the graph to indicate the fraction of 2-bromo-2-methylpropane molecules that have enough energy to react.

(b(ii))[2]

On the same axes, sketch the energy distribution for a sample of 2-bromo-2-methylpropane at $50\,^{\circ}\text{C}$.

(b(iii))[1]

State the effect of an increase in temperature on $E_a$ for this reaction.

(c(i))[3]

Draw the mechanism for the reaction of 2-bromo-2-methylpropane with $\text{OH}^- (aq)$. Show the intermediate produced in this reaction. Include all charges, partial charges, lone pairs and curly arrows where relevant.

(c(ii))[1]

Name the mechanism for this reaction.

(d)[2]

The experiment is carried out again at $25\,^{\circ}\text{C}$, but with 2-chloro-2-methylpropane used instead of 2-bromo-2-methylpropane. Keep all other variables unchanged. Predict how the time for the pink colour to disappear compares with the original experiment. Explain your answer.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: Amount of substance changed per unit time

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