CIE Nov 2015 v1 Paper 3 Q2

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PMT In this experiment you will investigate how the rate of reaction between sodium thiosulfate and hydrochloric acid is affected by the concentration of the acid. When aqueous thiosulfate ions react with hydrogen ions, H+, in any acid, a pale yellow precipitate of sulfur is formed. The ionic equation for this reaction is given below. S2O3 2(aq) + 2H+(aq)S(s) + SO2(aq) + H2O(l) The rate of the reaction can be determined by measuring the time taken to produce a fixed quantity of sulfur. FA 4 is 0.10 mol dm3 sodium thiosulfate, Na2S2O3. FA 5 is 0.20 mol dm3 hydrochloric acid, HCl. (a) Method Record all your measurements, in an appropriate form, in the space below. Experiment 1Use the larger measuring cylinder to transfer 40 cm3 of FA 4 into the 100 cm3 beaker. Rinse the larger measuring cylinder thoroughly with water, then add 30 cm3 of FA 5 to the beaker and start timing immediately. Stir the mixture once and place the beaker on top of the printed insert page provided. Look down through the solution in the beaker at the print on the insert. Stop timing as soon as the precipitate of sulfur makes the print on the insert invisible. Record the reaction time to the nearest second. Empty and rinse the 100 cm3 beaker. Dry the outside of the beaker ready for Experiment 2. Rinse the larger measuring cylinder, then use it to transfer 40 cm3 of FA 4 into the 100 cm3 beaker. Use the smaller measuring cylinder to add 10 cm3 of distilled water to the beaker. Use the same measuring cylinder to add 20 cm3 of FA 5 to the mixture in the beaker and start timing immediately. Stir the mixture once and place the beaker on top of the printed insert page provided. Stop timing as soon as the print on the insert becomes invisible. Record the reaction time to the nearest second. Empty and rinse the 100 cm3 beaker. Dry the outside of the beaker ready for Experiment 3. Carry out the reaction using a mixture of 40 cm3 of FA 4, 20 cm3 of distilled water and 10 cm3 of FA 5. Measure and record the reaction time to the nearest second.Experiment 2Experiment 3UCLES 2015 9701/31/O/N/15 [Turn over II III IV [4]<br /> PMT (b) (i) The rate of reaction can be represented by the formula below. rate of reaction = reaction time 1000 Use this formula to calculate the rate of reaction for Experiments 1 and 3. Give the unit. rate of reaction for Experiment 1unitrate of reaction for Experiment 3unit(ii) Calculate the initial concentrations of hydrochloric acid in the reaction mixtures in Experiments 1 and 3. initial concentration of HCl in Experiment 1 =mol dm3 initial concentration of HCl in Experiment 3 =mol dm3 (iii) How is the rate of reaction affected by the concentration of hydrochloric acid in the mixture?(iv) Predict how the reaction time measured in Experiment 1 would have been affected if the experiment had been carried out using 0.20 mol dm3 sulfuric acid instead of 0.20 mol dm3 hydrochloric acid. Explain your answer.(v) Predict how the reaction time measured in Experiment 3 would have been affected if the experiment had been carried out in a 250 cm3 beaker instead of a 100 cm3 beaker. Explain your answer.[5] [Total: 9]UCLES 2015 9701/31/O/N/15<br />

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