Halogenoalkanes undergo hydrolysis with aqueous sodium hydroxide to form alcohols. e.g. CH3CH2CH2CH2Br(l) + NaOH(aq) → CH3CH2CH2CH2OH(l) + NaBr(aq) A student carried out an experiment to compare the rate at which three halogenoalkanes, 1-chlorobutane, CH3CH2CH2CH2Cl, 1-bromobutane, CH3CH2CH2CH2Br, and 1-iodobutane, CH3CH2CH2CH2I, undergo hydrolysis. The method used was as follows: • Place a 5 cm³ sample of each halogenoalkane into separate test-tubes. • Add 1 cm³ of organic solvent to each test-tube. • Add 2 cm³ aqueous sodium hydroxide to each test-tube. • Add 3 drops of acid-base indicator to the mixture. • Heat the test-tubes in a thermostatically controlled, electrically heated water bath. • Record the time taken for the indicator to change colour.

1. (a)Give two reasons why the experiment was carried out using an electrically heated water bath.[2]
2. (b)Sodium hydroxide is corrosive. Apart from wearing safety glasses and a lab coat, state one safety precaution which must be taken when handling sodium hydroxide.[1]
3. (c)Suggest why an organic solvent must be used in this experiment.[1]
4. (d)Why is acid-base indicator added to the reaction mixture?[1]
5. (e)(i)The student obtained the following results. halogenoalkane | time taken for indicator to change colour/s | 1/time /s-1 ---|---|--- 1-chlorobutane | 417 | 1-bromobutane | 238 | 1-iodobutane | 135 | Complete the table to show `1/time`[1]
6. (e)(ii)`1/time` can be used to represent rate of reaction. Suggest what the `1/time` values tell you about the trend in carbon-halogen bond enthalpies.[1]
7. (f)Identify one additional variable that must be controlled in this experiment.[1]
8. (g)(i)The student decided to investigate the order of reaction with respect to aqueous sodium hydroxide. CH3CH2CH2CH2Cl(l) + NaOH(aq) → CH3CH2CH2CH2OH(l) + NaCl(aq) step 1 An excess of 1-chlorobutane was mixed with 1.00 mol dm-3 NaOH(aq), at room temperature. step 2 A stop-clock was immediately started. step 3 At intervals of 60 seconds the student took 10.00 cm³ samples from the reaction mixture, for 11 minutes. step 4 Each 10.00 cm³ sample was immediately added to ice in a conical flask. step 5 The concentration of NaOH(aq) in each sample was determined by titration. The results are shown. time/s | concentration of NaOH(aq)/mol dm-3 ---|--- 0 | 1.00 60 | 0.75 120 | 0.62 180 | 0.51 240 | 0.39 300 | 0.31 360 | 0.24 420 | 0.19 480 | 0.12 540 | 0.13 600 | 0.11 660 | 0.09 Plot a graph of concentration of NaOH(aq) (y-axis) against time (x-axis). Use a cross (x) to plot each data point. Draw a curved line of best fit.[2]
9. (g)(ii)Circle the point which you consider to be most anomalous.[1]
10. (g)(iii)Suggest one reason for this anomalous point.[1]
11. (g)(iv)Draw construction lines on the graph to calculate two consecutive half-lives for this reaction. first half-life = ...................................... s second half-life = ...................................... s [2][2]
12. (g)(v)State whether you consider this to be a first-order reaction with respect to NaOH. Explain your answer.[1]
13. (h)(i)The total volume of the reaction mixture at the start of the experiment was 250 cm³. Name a piece of apparatus that could be used to remove 10.00 cm³ samples from the reaction mixture.[1]
14. (h)(ii)Suggest why the student did not remove 25.00 cm³ samples for titration from the reaction mixture.[1]
15. (h)(iii)Explain why each sample is added to ice in step 4.[1]
16. (i)Another method for following the rate of a reaction is to measure changes in electrical conductivity. Explain why this would not be a suitable method for following this reaction.[1]