OCR A Jun 2011 Paper 5 Q3

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In aqueous solution, methanoic acid, HCOOH, reacts with bromine, Br2. HCOOH(aq) + Br2(aq) 2H+(aq) + 2Br (aq) + CO2(g) A student carried out an investigation on the rate of this reaction. The student used a large excess of methanoic acid which ensured that its concentration was effectively constant throughout. During the reaction, bromine is used up and its orange colour becomes less intense. The intensity of the bromine colour can be measured with a colorimeter to give the bromine concentration. The graph below was plotted from the experimental results. 0.010 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 100 200 300 500 600 700 400 time / s [Br2] / mol dm3OCR 2011<br />
 In this investigation, a large excess of methanoic acid was used. Under these conditions, the reaction is effectively zero-order with respect to methanoic acid.Using the graph, determine the order of reaction with respect to bromine.Using the graph, determine the initial rate of the reaction. Calculate the rate constant, k, for the reaction between methanoic acid and bromine under these conditions. (cid:4) In your answer you should make clear how your conclusions fit with the experimental results, including working shown on the graph and units where appropriate.[9]OCR 2011 [Total: 9] Turn over<br />

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