Chemistry 2021 · Oct/Nov · Paper 52

Halogenoalkanes undergo hydrolysis with aqueous sodium hydroxide to form alcohols. e.g. CH OH

+ NaBr(aq) A student carried out an experiment to compare the rate at which three halogenoalkanes, 1-chlorobutane, CH Cl, 1-bromobutane, CH Br, and 1-iodobutane, I, undergo hydrolysis. The method used was as follows: sample of each halogenoalkane into separate test-tubes. of organic solvent to each test-tube. aqueous sodium hydroxide to each test-tube.

Give two reasons why the experiment was carried out using an electrically heated water bath. 1 2

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.

Suggest why an organic solvent must be used in this experiment.

Why is acid-base indicator added to the reaction mixture?

The student obtained the following results. halogenoalkane time taken for indicator time 1-chlorobutane 417 1-bromobutane 238 1-iodobutane 135

Complete the table to show time

time can be used to represent rate of reaction. Suggest what the time values tell you about the trend in carbon-halogen bond enthalpies.

Identify one additional variable that must be controlled in this experiment. Question 2 continues on the next page.

The student decided to investigate the order of reaction with respect to aqueous sodium hydroxide. NaOH(aq), at room temperature. step 2 A stop-clock was immediately started. samples from the reaction mixture, for 11 minutes. 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. concentration of 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). NaOH(aq) / mol dm time / s 0 100 200 300 400 500 600 700 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10

Circle the point which you consider to be most anomalous.

Suggest one reason for this anomalous point.

Draw construction lines on the graph to calculate two consecutive half-lives for this reaction. first half-life = s second half-life = s

State whether you consider this to be a first-order reaction with respect to NaOH. Explain your answer. samples from the reaction mixture. samples for titration from the reaction mixture.

Explain why each sample is added to ice in step 4.

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. [Total: 19] Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every UHDVRQDEOHH?RUWKDVEHHQPDGHE\WKHSXEOLVKHU8&/(6WRWUDFHFRS\ULJKWKROGHUVEXWLIDQ\LWHPVUHTXLULQJFOHDUDQFHKDYHXQZLWWLQJO\EHHQLQFOXGHGWKH publisher will be pleased to make amends at the earliest possible opportunity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