Investigating the affect of concentration on the rate of reaction.

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Investigating the affect of concentration on the rate of reaction


This investigates how the rate of a chemical reaction depends on the concentration of reactants in the solution. This will be investigated with the following experiment in which dilute hydrochloric acid and sodium thiosulphate solutions are mixed. This forms insoluble sulphur and the mixture gradually becomes cloudy.

If the concentration of the sodium thiosulphate concentration is varied, the rate of production of sulphur can be measured by recording the time taken for the reaction mixture to go cloudy.

The rate of the formation of sulphur can be measured using a light sensor and measuring the time taken for the light transmitted through the solution to form by 10%.


Having set up the apparatus as shown in the given diagram, carry out the following steps.


1)Get the apparatus together and for the first experiment, measure the appropriate amount of the solutions (5cm" of hydrochloric acid, 50cm" of 0.15

molar sodium thiosulphate and 0cm" of water). Add the hydrochloric acid after the light has been trained onto the conical flask containing the other two solutions and the light getting through is at around 85%.

2)Then add the dilute hydrochloric acid and start the logit to collate the results.

3)Stop the logit after the amount has dropped to 75% of the light getting through to the sensor.

4)Then for the rest of the experiments remember the 5cm cubed of hydrochloric acid (it is 2molars in strength) and mix up the correct solution (amount 50cm") of sodium thiosulphate: water.

These are the ratios in which the solutions should be made:

ExperimentVolume of 0.15M sodium Volume of water

thiosulphate (cm") (cm")

1 50 0

2 40 10

3 30 20

4 20 30

5 10 40


As the reaction proceeds,