ACJC H2 Chem 2013 Prelim P3 QP

2 © ACJC 2013 9647/03/Prelim/13 [Turn over Answer any four questions. 1 (a) Liquid bromine is added to propenyl ethanoate CH 2=CHCH2OCOCH3 in presence of concentrated ethanoic acid which acts as a solvent, slowly enough for the reaction to be followed by usual laboratory techniques. The following results were obtained at 25 oC. Experiment Number [propenyl ethanoate]/mol dm-3 [Br2]/mol dm-3 Rate/ mol dm -3 s-1 1 4.0 x 10-2 2.0 x 10 -2 1.29 x 10 -3 2 6.0 x 10-2 2.0 x 10 -2 1.94 x 10 -3 3 4.0 x 10-2 4.0 x 10 -2 5.16 x 10 -3 [10] (i) Write the equation for the addition of bromine to propenyl ethanoate (ii) Deduce the order of reaction with respect to propenyl ethanoate and bromine and hence write the rate equation for the reaction. (iii) Estimate how long it would take for 1% of ester to react in Experiment Number 3. (iv) Experiment Number 1 was repeated with 2.0 x 10 -2 mol dm-3 bromine under the same experimental condition, but using 4.0 x 10-2 mol dm-3 CH2=CHCHClOCOCH3 instead. Would you expect any change to the rate? Suggest a reason for this change if any. (v) What would be the product if water were to be used as a solvent instead of concentrated ethanoic acid? (vi) Would you expect the rate of reaction to be slower or faster if aqueous bromine were to react with propenyl ethanoate? Suggest a reason. 286

3 © ACJC 2013 9647/03/Prelim/13 [Turn over (b) In an experiment, 50.0 cm 3 of aqueous magnesium chloride were titrated with 1.00 mol dm-3 sodium hydroxide. The pH of the solution changed as shown in the diagram below. [10] 287

4 © ACJC 2013 9647/03/Prelim/13 [Turn over (i) Calculate the initial concentration of magnesium chloride. (ii) When 10.0 cm3 of NaOH have been added, calculate the (a) hydroxide ion concentration (b) hydrated magnesium ion concentration Hence, calculate the solubility product of magnesium hydroxide. (iii) Suggest how, if at all, the pH of a saturated solution of Mg(OH) 2 would change if the temperature were to be increased given that Ksp of Mg(OH)2 decreases with increasing temperature. (iv) By means of an equation, explain why initial pH of graph starts at 6. [Total: 20 marks] 288

5 © ACJC 2013 9647/03/Prelim/13 [Turn over 2 (a) A cycloalkane, C 5H10, gives only two mono-brominated products (ignoring any stereoisomers) with Br2 under uv light. [3] (i) Give the structural formulae of the cycloalkane and the two mono- brominated products formed. (ii) Suggest the ratio in which the two mono-brominated products will be formed. (b) Cyclopentane is an isomer of the cycloalkane identified in (a)(i). It ca