Edexcel Jan 2017 (IAL) Paper 4 Q21

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 21 Crystal violet is an indicator which is coloured in solutions of acids, and colourless in alkalis. The kinetics of the reaction of crystal violet with sodium hydroxide were investigated. Using the abbreviation CV+ for the formula of crystal violet, a simplified equation for the reaction is CV+(aq) + OH(aq) (cid:111) CVOH(aq) violet colourless (a) Equal volumes of 0.100 mol dm3 sodium hydroxide and 5.00105 mol dm3 crystal violet were mixed. (i) Explain why very different concentrations of sodium hydroxide and crystal violet were used in the experiment to find the order with respect to crystal violet. (1)(ii) Suggest a method which could be used in this experiment to continuously monitor the change in concentration of crystal violet with time. (1)10 *P48372RA01028* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (iii) The graph shows how the concentration of crystal violet changes with time. [CV+(aq)] / 105mol dm3 2.52.01.51.00.50 0 10 15 20 25 30 Time / min Measure two half-lives for this reaction showing your working on the graph. Give the half-lives below. (2)(iv) Use your half-lives to deduce the order with respect to CV+. Justify your answer. (2)A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48372RA01128* 11 Turn over<br /> (b) In another series of experiments the rate constant was determined at different temperatures. The table shows the values of the rate constant, k, at different temperatures. Some of the corresponding values for the reciprocal of temperature and ln k are also shown. D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A (1) (5) (i) Complete the table by calculating the missing values. T/K 285 288 291 294 297 3.35103 4.30103 5.19103 6.67103 7.91103 1 T / K1 3.51103 3.47103 3.44103 3.40103 ln k 5.70 5.45 5.26 5.01 (ii) Plot a graph of ln k on the vertical axis against 1/T on the horizontal axis and calculate the gradient. 12 *P48372RA01228*<br /> A E R A S I H T N I E T I R W T O N O D GradientA E R A S I H T N I E T I R W T O N O D (iii) Use your value of the gradient in (b)(ii) to calculate the activation energy, Ea , of the reaction. Remember to include units with your answer, which should be given to two significant figures. The Arrhenius equation is ln =E a R 1 T + constant . 8 3 1 J mol11 (2) A E R A S I H T N I E T I R W T O N O D (Total for Question 21 = 14 marks) *P48372RA01328* 13 Turn over<br /> D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A BLANK PAGE 14 *P48372RA01428*<br />

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