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Rates of reaction Sodium Thiosulphate and Hydrochloric Acid An experiment was carried out to investigate the effect of temperature on the rate of reaction between sodium thiosulphate and hydrochloric acid. The equation for this reaction is shown below.

Method (1) A measuring cylinder was used to measure 50cm3 of 0.08M sodium thiosulphate solution into a test tube. A bung was placed in the test tube. (2) A pipette was used to measure 5cm3 of 1.0M hydrochloric acid and this was placed into a second test tube. A bung was placed in the test tube. (3) Both test tubes were placed into a water bath thermostatically controlled to be at 400C. (4) An “x” was drawn onto a piece of paper and a 100cm3 beaker was placed onto it. (5) The sodium thiosulphate and hydrochloric acid in the test tubes were poured into the beaker and the timer was started. (6) The timer was stopped when the “x” was no longer visible when viewed from above. (7) The experiment was repeated at 50, 60, 70 and 800C. Results Experiment number 1 2 3 4 5 Temperature (0C) 40 50 60 70 80 Time for X to disappear (s) 25 20 16 11 7 1/time

Analysis and Evaluation questions (1) Complete the missing column on the results table. (2) Draw a graph of temperature (x-axis) against 1/time (y-axis) (3) The experiment carried out is an investigation into rate of reaction. How do we measure rate of reaction? What units are used?

(4) When in the reaction is the rate of reaction fastest? What is this called? How is it defined?

(5) Which of the reactants or products are being used to measure the rate of this chemical reaction?

(6) 1/time is approximately proportional to the initial rate of reaction. Explain why this is the case.

(7) What assumptions are made to be able to state that 1/time is proportional to the initial rate of reaction?

(8) Why do you think that 1/time is only “approximately proportional to the initial rate of reaction?

(9) Use your graph to draw a conclusion about the change of the...
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