The variable I am choosing to alter is the ratio of sodium thiosulphate to water because it is the easiest and safest to control and measure. It will also give the most accurate results.
Step by Step plan:
- Mix together 10ml of HCl and a preset amount of sodium thiosulphate solution in a flask and place the piece of paper with a cross on underneath.
- Time how long it takes for the cross to ‘disappear’. Record the results.
Fair Test:
I will keep this experiment a fair test by controlling as many variables as possible:
- Temperature
- Amount of hydrochloric acid
- Concentration of the hydrochloric acid
- Number of times stirred
It is important to keep these variables the same because otherwise it will affect my results’ accuracy.
Safe Test:
I will make sure the experiment is conducted safely by making sure all involved are wearing safety goggles and that the workspace is clear.
Prediction:
I predict that the highest concentration will have the fastest reaction time because there are more particles to react with.
Results:
Chart of Results:
Conclusion:
My results show that the rate of reaction was affected by the concentration of the sodium thiosulphate. The relationship between the concentration of sodium thiosulphate and the rate of reaction is that if you increase the concentration of the sodium thiosulphate, the rate of reaction increases because there are more particles for the hydrochloric acid to react with. This increased the rate of reaction because it was more likely that the particles would collide with enough force that they would react. My prediction was partly correct. I believe that the concentration ‘6’ should have been closer to 33.5 than 28, however this doesn’t make too much difference to my results.
Evaluation:
I think that my experiment was, on the whole, a fair test. There was a slight discrepancy but this did not affect my results too much. I believe that the anomalous results were caused by contaminated equipment. I think that my results were accurate because they were repeated several times. I could have improved my investigation by using sterile equipment. I could also used different flasks each time to prevent contamination. If I had used smaller flasks, the reaction would have probably worked better.
