12   4 This question is about halogenoalkanes and some of their reactions. (a) X, Y and Z are three different halogenoalkanes. X is 1‑chloropropane Y is 1‑bromopropane Z is 1‑iodopropane An experiment is carried out to compare the rates of hydrolysis of these compounds. Outline procedure: 1 cm3 of each of the three halogenoalkanes, X, Y and Z, is added to separate test tubes, each containing 5 cm3 of ethanol and 5 cm3 of aqueous silver nitrate solution, in a water bath at 50 °C. The time taken for a precipitate to form in each test tube is measured. (i) Give three reasons why these reaction conditions are specified. 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(ii) Explain why a precipitate forms. 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Turn over 13   (iii) The three halogenoalkanes were placed in order of increasing rate of reaction. Which is the correct sequence? (1) A X, Y, Z B X, Z, Y C Y, X, Z D Z, Y, X (b) The results table shows the time taken to produce a precipitate when three bromoalkanes react with aqueous ethanolic silver nitrate solution. Halogenoalkane Time to produce a precipitate / s 1‑bromobutane 58 2‑bromobutane 33 2‑bromo‑2‑methylpropane 2 Give a reason why the times taken to produce a precipitate for these isomeric bromoalkanes are different. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 14   (c) (i) Which equation shows the first step of the mechanism for the reaction of 1‑bromopropane with ammonia? (1) A CH3 CH2 CH2 Br δ+ δ– CH3 CH2 CH2 NH2 + HBr • •NH3 B CH3 CH2 CH2 Br δ+ δ– CH3 CH2 CH2 NH3 + Br • •NH3 + – C CH3 CH2 CH2 Br δ+ δ– CH3 CH2 CH2 NH2 + Br • •NH3 + – D CH3 CH2 CH2 Br δ+ δ– CH3 CH2 CH2 NH3 + Br • •NH3 (ii) Write the formula of the final inorganic product of the reaction of 1‑bromopropane with excess ammonia. (1) .................................................................................................................................................................................................................................................................................... Turn over 15   (iii) The infrared spectrum of ethylamine is shown. 4000 3000 2000 1500 1000 500 Wavenumber / cm–1 100 50 0 Transmittance / % P S R Q Which absorption peak confirms this as an amine? (1) A absorption P B absorption Q C absorption R D absorption S (d) 1-bromopropane undergoes reactions when heated with different reagents. (i) Give two reasons why organic reactions are often heated for a long time but the yield is frequently low. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 16   (ii) Give the name or formula of the reagent and the condition, other than heat, used to increase the carbon chain length by one carbon atom, starting from 1-bromopropane. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iii) 1-bromopropane, CH3CH2CH2CH2Br, can be converted into but-1-ene, CH3CH2CH CH2 . Give the name or formula of the reagent and the condition, other than heat, used for this reaction. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 4 = 16 marks) Turn over 17   BLANK PAGE