AQA AS Specimen Paper 2 Q7

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16 A student carried out an experiment to determine the number of C=C double bonds in a molecule of a cooking oil by measuring the volume of bromine water decolourised. The student followed these instructions:Use a dropping pipette to add 5 drops of oil to 5.0 cm3 of inert organic solvent in a conical flask.Use a funnel to fill a burette with bromine water.Add bromine water from a burette to the solution in the conical flask and swirl the flask after each addition to measure the volume of bromine water that is decolourised. The students results are shown in Table 2. Table 2 Experiment Volume of bromine water / cm3 39.40 43.50 41.20 0 7 . 1 In a trial experiment, the student failed to fill the burette correctly so that the gap between the tap and the tip of the burette still contained air. Suggest what effect this would have on the measured volume of bromine water in this trial. Explain your answer. [2 marks] . 2 0 7 Other than incorrect use of the burette, suggest a reason for the inconsistency in the students results. [1 mark] Barcode Typesetter code<br /> 17 . 3 0 7 Outline how the student could improve this practical procedure to determine the number of C=C double bonds in a molecule of the oil so that more consistent results are obtained. [4 marks] . 4 0 7 The oil has a density of 0.92 g cm3 and each of the 5 drops of oil has a volume of 5.0102 cm3. The approximate Mr of the oil is 885 The concentration of bromine water used was 2.0102 mol dm3. Use these data and the results from experiment 1 to deduce the number of C=C double bonds in a molecule of the oil. Show your working. [5 marks] Barcode Number of C=C double bonds = Typesetter code Turn over <br />

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