Edexcel Jan 2016 (IAL) Paper 4 Q16

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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 SECTION B Answer ALL the questions. Write your answers in the spaces provided. 16 Bromine reacts with methanoic acid as shown below. HCOOH(aq) + Br2(aq) (cid:111) 2H+(aq) + 2Br(aq) + CO2(g) The kinetics of the reaction can be investigated by various methods. (a) For two different named substances, identify a method of following the progress of the reaction. The methods given should be different for each substance and should not involve taking samples from the reaction mixture. (2) Substance 1MethodSubstance 2Method(b) In an investigation of the kinetics of the reaction, a large excess of methanoic acid was used. (i) Use the data shown on page 12 to plot a graph that can be used to determine the order of reaction with respect to bromine. (2) A E R A S I H T N I E T I R W T O N O D *P46940A01128* 11 Turn over<br /> Time / s 60 120 180 240 300 420 600 700 [Br2(aq)] / mol dm3 0.0100 0.0082 0.0066 0.0053 0.0043 0.0034 0.0021 0.0011 0.0007 12 *P46940A01228* 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 /> A E R A S I H T N I E T I R W T O N O D (ii) Use the graph to confirm that the reaction is first order with respect to bromine. Show on the graph the measurements you use to confirm this and explain how the order is deduced. (3)(iii) Under the conditions of the experiment, the order of reaction with respect to methanoic acid appears to be zero. Explain why this is the case. (1)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 (iv) Further experiments show that the reaction is actually first order with respect to methanoic acid. Write the rate equation for the reaction. (v) The initial rate of the reaction carried out in part (b)(i) was found to be 4.54105 mol dm3 s1. The initial concentration of methanoic acid was 0.500 mol dm3 and that of bromine was 0.0100 mol dm3. Use these values, and your rate equation in part (b)(iv), to calculate the rate constant for the reaction. Give the units of the rate constant. (1) (2) I E T I R W T O N O D (Total for Question 16 = 11 marks) *P46940A01328* 13 Turn over<br />

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