24 7 Halogenoalkanes react with water to produce alcohols and halide ions. C4H9X  +  H2O  →  C4H9OH  +  X−  +  H+ (a) Test tube experiments can be carried out to investigate the relative rates of these substitution reactions. The halogenoalkanes 1‑chlorobutane, 1‑bromobutane and 1‑iodobutane can be used. Some of the steps in these experiments are ● each halogenoalkane is added to a different tube containing 1 cm3 of ethanol ● the test tubes are placed in the same beaker of hot water ● aqueous silver nitrate is added to each tube and the tubes are shaken ● a precipitate forms in each tube. (i) State the purpose of adding ethanol to each of the test tubes. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) Give one reason why the test tubes were put in the same beaker of hot water. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iii) Give one reason why the test tubes were shaken after the addition of aqueous silver nitrate. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 25 Turn over (b) (i) State how the halogen atom present in each halogenoalkane can be identified using observations from this experiment in (a). 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(ii) Identify further reagents that can be added, including relevant observations, to confirm the identity of the halogen atom present in each halogenoalkane. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 26 *(c) Outline the method for a test tube experiment, which expands on the steps in (a), to investigate how the rate of the substitution reaction depends on whether the halogenoalkane is primary, secondary or tertiary. Your experiment should test a series of isomeric bromoalkanes reacting with water. Your plan should include ● the chemicals you will use ● an outline of how the experiment will be carried out ● the observations or measurements you will make and how you will interpret them. 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(Total for Question 7 = 12 marks) TOTAL FOR PAPER = 80 MARKS 28