A large excess of 2-bromo-2-methylpropane is added to 0.0010mol of NaOH(aq), which contains a few drops of phenolphthalein indicator. A stopwatch is started as soon as the substances are mixed. The time taken for the pink colour to disappear is recorded. The experiment is repeated at different temperatures, keeping all concentrations and volumes of reagents constant. temperature /°C | time taken for pink colour to disappear/s 20 | 300 25 | 65 35 | 20 [Figure showing Maxwell-Boltzmann distribution curve with Ea marked] proportion of molecules with a given energy 0 Ea molecular energy

1. (a)Explain what is meant by the term rate of reaction.[1]
2. (b)(i)Label the graph to show the proportion of 2-bromo-2-methylpropane molecules which have sufficient energy to react.[1]
3. (b)(ii)Use the same axes to sketch the distribution of energies of molecules in a sample of 2-bromo-2-methylpropane at 50°C.[2]
4. (b)(iii)State the effect of an increase in temperature on Ea for this reaction.[1]
5. (c)(i)Draw the mechanism to show the reaction of 2-bromo-2-methylpropane with OH-(aq). Show the intermediate formed in this reaction. Include all charges, partial charges, lone pairs and curly arrows as appropriate. CH3 Br. CH3 H3C[3]
6. (c)(ii)Name the mechanism for this reaction.[1]
7. (d)The original experiment is repeated at 25°C with 2-chloro-2-methylpropane instead of 2-bromo-2-methylpropane. All other variables remain constant. Predict the effect of using 2-chloro-2-methylpropane compared to 2-bromo-2-methylpropane on the time taken for the pink colour to disappear. Explain your answer.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.