Investigate what happens to the rate of reaction when the concentration of Sodium Thiosulphate is altered in the reaction between Sodium Thiosulphate and Hydrochloric acid.

Method

Equipment needed

• 1 Bottle of Sodium Thiosulphate
• 1 Bottle of Hydrochloric Acid
• Water
• 1 Beaker
• 2 pipettes
• 2 measuring cylinders
• Goggles
• Paper with “X” mark
• Stop clock

In order for me to carry out my experiments I would need to change the concentration of Sodium Thiosulphate in the reaction between Sodium Thiosulphate and Hydrochloric Acid. I would do this by keeping the total volume of the reactant 50³ all the time. I would change the concentration of Sodium Thiosulphate by decreasing the volume of Sodium Thiosulphate and increasing the volume of water in ten different experiments. In each of the experiments I would keep the amount of Hydrochloric acid the same and this would be 5cm³. Below is a table of how I would do this.

In order for me to get an accurate result, I am going to carry out these experiments three times. I will then work out the average result for all three and use that to create my graph which will tell me how the rate of reaction is affected by using different concentrations.

In order for me to carry out my experiments I would need to follow the following procedures…

1. Draw out an “X” on a paper and place it underneath the empty beaker.
2. Measure out the amount of Sodium Thiosulphate needed in one of the measuring cylinders and then insert it into the beaker.
3. Measure out the amount of water needed in the other measuring cylinder and insert it into the beaker with Sodium Thiosulphate.
4. I would then measure out 5cm³ of Hydrochloric acid with one of the pipettes and as soon as I add it to the beaker with water and Sodium Thiosulphate I would start the stop clock.
5. I will then time how long it would take the “X” on the paper to disappear. When it does I would stop the stop clock and note the time taken.
6. After finishing on experiment I would clean out the beaker and dry it out. I would then start the next experiment.

Diagram of experiment and equipment used

Safety

Whilst doing my experiments I would ensure that the following safety aspects are met…

• Bags and jackets are out of the way.
• Goggles are on to protect the eyes.
• If any liquid is spilled I would clean it up straight away.
• If any chemical is spilled on the body, I would wash it straight away.

Fair testing

To make my test fair I am only going to change one aspect that will affect the rate of reaction. I will continuously change the concentration of Sodium Thiosulphate and keep the following the same…

• The temperature.
• I will not use a catalyst.
• I will also use the same equipment and use the same paper with the “x” mark on it. The reason for this is because if I change the paper, it would affect the results because the “x” might be darker or lighter and this would take the “x” more or less time to disappear than the original paper.

I would also do the following to make the test a fair test…

• Use two different pipettes and measuring cylinders for each substance so that the reaction does not take place in them.
• After finishing an experiment I would clean out and dry the beaker so that there is no reacted substance left in the beaker.
• I would also make sure that all the measurements are accurate in order for me to get accurate results.

Results

Result 1

Result 2

Result 3

Average result

To work out the average result I added the time taken for 1 experiment from the three results, I then divided the total by 3. For example, for the first experiment these were my results,

Result 1: 0.4885

Result 2: 0.4507

Result 3: 0.4729

Average= 0.4885+4507+4729=1.4121

         = 1.4121/3

         =0.4707

Below are my average results for all the experiments I did.

From theses results I am now going to draw a scatter graph with a smooth line which will show me if the concentration affects the rate of reaction.

Conclusion

My smooth line on my graph of results clearly shows that concentration of a substance does have an effect on the rate of reaction. The graph shows that my prediction was correct, which was that as the concentration of Sodium Thiosulphate decreases the rate of reaction increases.

Evaluation

All my experiments went very well as there was not any mistakes made. I ensured that the fair testing and safety details listed above were met.

Overall I think my results were very accurate as I got 3 results and worked the average for all of them, which I then used to create my graph. I also believe that my results were accurate because on my graph there were not any anomalous results. I ensured that the equipment, mainly the beaker was cleaned after an experiment.

If I had more time I would improve my investigation by measuring out the substances used very accurately and also not to rush my experiments so that I could have more accurate results.    

Overall I think my investigation went very well. I got the results needed to answer my prediction and the coursework aim. I also think my results were accurate.