AQA AS Specimen Paper 1 Q4

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Colourless solutions of X(aq) and Y(aq) react to form an orange solution of Z(aq) according to the following equation. X(aq) + 2Y(aq) Z(aq) H = 20 kJ mol1 A student added a solution containing 0.50 mol of X(aq) to a solution containing 0.50 mol of Y(aq) and shook the mixture. After 30 seconds, there was no further change in colour. The amount of Z(aq) at equilibrium was 0.20 mol. . 1 Deduce the amounts of X(aq) and Y(aq) at equilibrium. 0 4 [2 marks] Amount of X(aq) = mol Amount of Y(aq) = mol . 2 0 4 On the grid below, draw a graph to show how the amount of Z(aq) changed from the time of initial mixing until 60 seconds had elapsed. [3 marks] Barcode Typesetter code<br /> . 3 0 4 The student prepared another equilibrium mixture in which the equilibrium concentrations of X and Z were: X(aq) = 0.40 mol dm3 and Z(aq) = 0.35 mol dm3. For this reaction, the equilibrium constant Kc = 2.9 mol2 dm6. Calculate a value for the concentration of Y at equilibrium. Give your answer to the appropriate number of significant figures. [3 marks] [Y] = mol dm3 0 4 . 4 The student added a few drops of Y(aq) to the equilibrium mixture of X(aq), Y(aq) and Z(aq) in Question 4.3. Suggest how the colour of the mixture changed. Give a reason for your answer. [3 marks] Colour change Reason . 5 0 4 The student warmed the equilibrium mixture from Question 4.3. Predict the colour change, if any, when the equilibrium mixture was warmed. [1 mark] Barcode Typesetter code Turn over <br />

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