# An experiment to investigate the effect of changing the concentration

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An experiment to investigate the effect of changing the concentration of hydrochloric acid on the rate of reaction with sodium thiosulpahte.

Aim

I am trying to find out how the concentration of hydrochloric acid affects the reaction time with sodium thiosulpahte.

If a clear solution of sodium thiosulphate is mixed with hydrochloric acid then a reaction will occur where a creamy-yellow precipitate of sulphur is produced.

H20

Text Box: + Text Box: + Text Box: + Na2S203 2HCL

Text Box: + 2NaCl SO2 S

Reactants Products

The sulphur takes a while to form and starts to turn the water cloudy after a short time. You cannot tell when the reaction has stopped so a cross drawn on a piece of paper in pencil can be
They all increase the number of collisions.

Fair testing

* To make this a fair test I will only change one variable.

* Each experiment will be done three times so an average can be found.

* The same equipment will be used in each experiment.

Method

· Measure out 50ml of thiosulphate and add it to the conical flask.

· Draw a cross on a piece of paper and place the conical flask on it.

· Measure out 10ml of acid and add it to the conical flask and start timing.

· Look into the top of the conical flask and when the cross can no longer be seen stop the stop watch.

· Do the experiment again but measure out 8ml of hydrochloric acid. Then add 2ml of distilled water. The ratio for each experiment will therefore be 10:0, 8:2, 6:4, 4:6 and of acid to water

Conclusion

I conclude that whilst carrying out this investigation I found out that the more acid was in the solution the cross on the paper disappeared quicker. This shows that the more concentrated the acid is then the quicker the reaction time. My research about the collision theory was correct and the more concentrated the solution is then the number of collisions will be increased. If the numbers of collisions are increased then the reaction time will also be increased.

My prediction 'that the less concentrated the acid is then the longer it will take for the sodium thiosulphate to react with the acid' is correct because experiment number 5