GCSE Science Coursework - Investigating the factors that affect the reaction between sodiumthiosulphate and hydrochloric acid

Essay by EddeyHigh School, 10th gradeB, October 2006

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Investigating the factors that affect the reaction between sodiumthiosulphate and hydrochloric acid


To investigate the differences in rate of reaction between sodiumthiosulphate and hydrochloric acid as the concentration of sodiumthiosulphate is either raised or lowered while keeping the total volume of the sodiumthiosulphate solution at 50cm .

The chemical reaction for this experiment is:


I start with 5cm of hydrochloric acid to which I add a varying concentration of sodiumthiosulphate. To change the STS (sodiumthiosulphate) concentration I will add 10cm of water to a fresh flask of STS after each experiment while each time reducing the volume of STS by the same amount. I will be measuring the results by timing the reaction until the solution is too 'cloudy' and filled with sodium for an image underneath the flask to be seen. I am allowing up to three minuets for this reaction to take place, after which time the concentration will simply be marked as over three mins.

Using this method my final results table will read as follows:

Volume of Sodiumthiosulphate Volume of Water Concentration of Solution (Molar) Results - Time Taken

50cm 0cm 0.2m

40cm 10cm 0.16m

30cm 20cm 0.12m

20cm 30cm 0.08m

10cm 40cm 0.04m

Using a table as seen above allows me to make a graph displaying the correlation between the different values used in the experiment once I have filled in my results column.


To conduct this experiment I will need:

Approximately 150cm of STS

Approximately 25cm of acid and

Approximately 100cm of water

These volumes of STS, water and acid will be enough for me to run one batch of experiments, these amounts might need to be increased by up to three times to accurately carry out the experiment. As well as the liquids I will also need:

Conical Flasks

Measuring Cylinder


Safety Goggles

I predict that as the solution of STS becomes less concentrated the rate of reaction will slowdown and may exceed the time limit for the experiment.