Water
The only variable will be the volume of sodium thiosulphate.
The thing I will not change is the volume of hydrochloric acid.
I will measure the speed of reaction by timing it using a fairly reliable stopwatch to a hundredth of a second. I will measure the volume of hydrochloric acid 5 ml measuring cylinder and the sodium thiosulphate using a 50 ml measuring cylinder.
For safety reasons I will wear a pair of goggles as I am going to be using chemicals, and mixing them together to look out for any reactions.
I will have to be very careful when pouring the acid and the sodium thiosulphate solution, because it could really be dangerous if it fell on anyone or myself.
Method:
Firstly I will collect all my measuring apparatus and materials that my experiment is based around- here it is sodium thiosulphate and hydrochloric acid.
For the first test I will measure the specified measurements for sodium thiosulphate and hydrochloric acid. (water isn’t needed in the first test) and place the piece of paper or tile with a cross-marked on it under the beaker. Once I have poured Sodium thiosulphate and hydrochloric acid into the beaker I will start timing straight away and wait until the cross on the piece of paper or tile can’t be seen from a birds eye view of the beaker.
Then once I am really sure that the cross has disappeared from the sulphur clouding up, I will stop timing and then record the results.
For the remaining number of tests I will do exactly the same, but I will increase the amount of Sodium of thiosulphate but add and increase the volume of water. And record all the results into a table.
I didn’t make any major or minor changes from my plan in the beginning, I stuck to the structure of my plan so it was much easier to do the final experiment.
This graph shows the results of my experiment (also shown in the table above) in a scatter diagram. The experiment was repeated under the same conditions so we can compare results and calculate an average. The line of best fit shows the moving average for both experiments on the graph so more points needn’t be plotted for the average.
After completing the experiment I found out that the stronger the concentration of sodium thiosulphate the quicker there was a chemical reaction between hydrochloric acid and sodium thiosulphate solution, but as the water was increased in the beaker, the chemical reaction became weaker and slower as the hydrochloric acid and sodium thiosulphate became dilute. My prediction was proved correct.
There was a similar pattern shown in the graph between the two experiments, the points were plotted on the graph, which had a negative correlation. The curve sloped downwards.
When the sodium thiosulphate solution and the hydrochloric acid were poured into the beaker the sulphur clouded up very quickly, the table and graph shows that both experiments they clouded up under a minute. But when the water is added and the hydrochloric acid and sodium thiosulphate solution became dilute and the reaction slowed down.
I think my results were fairly reliable, because I used the apparatus that were quite basic and easy to use. So I think my results are quite accurate as I measured the liquids in millilitres and the time in minutes and to the closest hundredth of a second.
All the results fit the same pattern and sloped down the same way.
If f I were to repeat the experiment then I would like to use computerised apparatus so the results are more accurate. A computer could time it more accurately and start timing straight away and stop when the cross wasn’t visible.
To extend this work I can plan to experiment how fast the reaction is under different temperatures.
