Edexcel Jan 2016 (IAL) Paper 4 Q20

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(e) A buffer was made by mixing 20 cm3 of 0.050 mol dm3 sodium hydroxide and 20 cm3 of 0.25 mol dm3 propanoic acid. (i) Write the equation for the reaction between sodium hydroxide and propanoic acid. State symbols are not required. (1) D O N O T W R I T E I (ii) Calculate the pH of this buffer solution. Show your working. Refer to your Data Booklet where needed. 20 *P46940A02028* N T H I S A R E A (5) 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 /> A E R A S I H T N I E T I R W T O N O D (iii) Explain how this solution acts as a buffer when a small amount of alkali is added. Include any relevant equations in your explanation. (3)(Total for Question 19 = 15 marks) TOTAL FOR SECTION B = 51 MARKS 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 *P46940A02128* 21 Turn over<br /> Answer ALL the questions. Write your answers in the spaces provided. 20 Nitrogen monoxide, NO, reacts with oxygen as shown below. SECTION C NO(g) + O2(g) (cid:111) NO2(g) (cid:507)H (cid:57) = 57 kJ mol1 (a) (i) Calculate the standard entropy change of the system, (cid:507)S (cid:57) system. The standard molar entropy of O2(g) is 102.5 J mol1 K1. Use other standard molar entropy values from your Data Booklet. Include a sign and units in your answer. (ii) Calculate the entropy change of the surroundings, (cid:507)S (cid:57) hence the total entropy change, (cid:507)S (cid:57) total at this temperature. surroundings at 298 K and Include a sign and units in your answers. (iii) Calculate the temperature at which the reaction ceases to be spontaneous. 22 *P46940A02228* D O N O T W R I T E I N T H I S A R E A (2) D O N O T W R I T E I (2) (2) 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 /> A E R A S I H T N I E T I R W T O N O D (b) Nitrogen monoxide and carbon monoxide are formed in car engines. To prevent these pollutant gases being released into the atmosphere, car exhausts are fitted with a catalyst and the reaction below occurs. CO(g) + NO(g) (cid:111) CO2(g) + N2(g) At the temperature of the car exhaust, (cid:168)Stotal for this reaction is positive. Suggest why this reaction needs a catalyst. (1)(Total for Question 20 = 7 marks) 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 *P46940A02328* 23 Turn over<br />

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