Edexcel Jan 2017 (IAL) Paper 4 Q23

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23 This question is about lactic acid, CH3CH(OH)COOH (a) Give the IUPAC name for lactic acid. (1)(b) Write the equation for the reaction of lactic acid with excess phosphorus(V) chloride, PCl5, showing the structural formula of the organic product. State symbols are not required. (c) The acid dissociation constant, Ka, of lactic acid is 1.38104 mol dm3. (i) Write the expression for the acid dissociation constant of lactic acid. (ii) State whether lactic acid is a stronger or weaker acid than ethanoic acid. Quote data from page 18 of your Data Booklet to justify your answer.18 *P48372RA01828* 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 (3) (1) (1)<br /> (iii) Calculate the pH of a 0.150 mol dm3 solution of lactic acid, giving your answer to two decimal places. State two assumptions you have made. (4) Assumptions(iv) A buffer solution with a pH of 4.00 is prepared using lactic acid and sodium lactate, CH3CH(OH)COONa. Calculate the mass of sodium lactate that should be dissolved in 1.00 dm3 of 0.150 mol dm3 solution of lactic acid to make a buffer solution of pH 4.00. Sodium lactate has molar mass of 112 g mol1. (4) 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 *P48372RA01928* 19 Turn over<br /> *(v) A small volume of hydrochloric acid is added to the buffer solution made in (c) (iv). Explain why the pH of the solution does not change significantly. Include an equation when you refer to any reaction which occurs. (3)D O N O T W R I T E I N T H I S A R E A(Total for Question 23 = 17 marks) TOTAL FOR SECTION B = 48 MARKS 20 *P48372RA02028* 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 />

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