Changing the rate of a reaction by changing the concentration:

The following apparatus will be needed for this task:  

• Measuring cylinder
• Conical flask
• Stop clock
• White paper
• Marker

Method:

• A cross is marked on a piece of paper.
• Using a measuring cylinder, measure out 25ml of sodium thiosulphate and pour that into the conical flask and put on top of the paper. The cross should be easy to see through the solution, from above.
• 40ml of hydrochloric acid is added quickly, and a clock started at the same time. The cross grows fainter as the precipitate forms.
• The clock is stopped the moment the cross can no longer can be seen from above and record the time.
• Repeat the experiment several times using different concentrations (2%, 4%, 8%, 12% and 16%) of sodium thiosulphate. The temperature of each reactant is kept exactly the same each time. Only the concentration of sodium thiosulphate is changed.
• Represent your results in a table.

 

The first set of results:

The second set of results:

The average table:

By looking at all of the results we can understand that the more the concentration of the sodium thiosulphate, the less time will take for the cross to grow fainter. Therefore the less the concentration of the sodium thiosulphate (e.g. 2%), the more time will take for the cross to grow fainter. The more the percentage of the sodium thiosulphate (more concentration, concentrated in the solution) hence more collision will take place which means more energy will be given to the particles by rubbing to each other, therefore less time will take for the cross to go fainter.

Fair Test: To make the test fair, I did the experiment several times (as you can see I have two tables for two sets of results) and I made a separate table to find the average of the two tables which gives us clear understanding of the results and conclusion. So in this way my results are more accurate and reliable.

Graphs for the results of the average table (XY Scatter):

Another type of graph (line graph) for the average table:

Improvement: To improve the test we can repeat the test several times. Foe example I have 2 sets of results, by repeating the test I will have more results which means I will have more clear idea about the results and the average will be more accurate and reliable.