This was the result of my preliminary work:
These results are suitable for this experiment. This is because I Will be able to do a full set of results within an hour (This is my given time period) I chose to do both 10cm³ of acid and 15cm³ of acid to see which of the two would give a better result..
From my preliminary results I decided that it would be best to used 15cm³ of acid because it reacted with the sodium thiosulphate. Also I realised that every time I had done an experiment, I would need to thoroughly clean out the test tube(s). This was because some of the residue from the other experiment was left in the test tube making the reaction happen in an unrealistic time and also causing the results to be wrong.
From the results of my preliminary work I have chosen to use 15cm³ of acid. This was because the time taken was longer with the 10cm³. Although this reaction would have been sufficient for my experiments, I felt that if I used 15cm³ of acid I would be able to do more experiments in less time.
We also chose to do the experiments at room temperature, the temperature needs to be kept constant so that the reaction does not speed up or down. If this was to happen we would have to re-do the experiment. This is because it would not be a fair test.
Method:
- Collect equipment and set up as shown on the diagram
- Add the 15cm³ of acid to the beaker
- Add the desired amount of solution (water and sodium thiosulphate)
- Put the beaker on top of the X.
- Time (with a stop clock) the time it takes for the X to become invisible
- Record results and Repeat.
Diagram:
Fair test points:
- Make sure you use the same amount of acid
- Make sure the same overall amount of solution (water and Sodium thiosulphate)
- Use the same X
- Use the same glass beaker
- Same temperature(20˚)
- 1.It has to stay at the same temperature so that there is no change in speed of the reaction. If the temperature changes, the results could change and ruin the experiment.
- 2.You have to use the same beaker, if you use a beaker that has a bigger or smaller capacity it will change the results due to the difference in surface area.
- 3.If a different X is used, this would cause the results to differ due to the different thicknesses of lines.
Safety Points:
- Always use goggles
- Do not get the solution on your hands, on skin or in your eyes.
- Do not spill the solution
- Tie hair back
- Make sure your tie is tucked in.
Results:
Graph:
Evaluation:
During my experimenting, I found only one anomalous result. I noticed this result because it was not on the line of best fit. This could have been caused by the fact that we used different people to witness the cross disappearing. This gives different judging from the witnesses. To improve this I could use a light sensored data logger or a video camera. Another improvement would be to use a different glass beaker every time instead of washing the same one out after each experiment. This could leave some residue and cause to reaction to differ.
Conclusion:
My results showed that as more sodium thiosulphate is added, the faster the rate of reaction is. This is because more particles are colliding with the acid. In other words the collision theory.
Low Concentration of Sodium High Concentration of Sodium
Thiosulphate. Thiosulphate.
There are more sodium thiosulphate particles reacting with the acid particles, making the reaction faster.