Stirring
Stirring the reaction then the atoms move around more and bang into each other more, thus speeding up the reaction. It is difficult to measure how much you stir something and is therefore not the best variable to test.
Surface Area
Changing the surface area effects the speed of the reaction because a change in area gives either more or less area for the reactions to take place on. But as the mass of the calcium carbonate is so small the pieces would be very difficult to measure accurately.
Pressure
Changing the pressure the reaction is taking place under is not possible to test in the school facilities so we can not do this experiment.
Catalyst
Using a catalyst would change the speed of the reaction relevant to its elemental properties. This could be done using the facilities at school.
For my investigation I have chosen to change the concentration of the acid because it is possible to do under the conditions available at school and is relatively easy to perform in the short amount of time we have to complete the task in.
Prediction
Higher concentration = more particles. The particles there are the more points of reaction there are, therefore my prediction is that the higher the concentration of the acid, the faster the reaction.
Plan
Aim
To find out how the concentration of acid affects the rate of a chemical reaction.
Diagram
Method
For my investigation I will set me apparatus up as above. I will then add 10cm3 of hydrochloric acid and 0.6g of calcium carbonate to the boiling tube. Then using a stopwatch I will time for 1 minute and then record the measurement on the gas syringe. I will then repeat the experiment for acid concentrations 0.5m, 1.0m, 1.5m and 2.0m.
So I get an accurate set of results I will test each concentration of acid 3 times and then find an average. For Safety I will need to wear safety glasses in order to prevent the acid from spitting up into my eyes during the experiment.
Fair Test
So that my experiments are fair I will need to keep the other variables the same. I will keep the temperature at 25oC (room temperature) the mass of the calcium carbonate at 0.6g with the same surface area (powder), The volume of acid at 10cm3, I will not stir the solution and I will keep the pressure constant (gravity) and I will not use a catalyst.
Results
Graph
Evaluation
The results we obtained in the end were satisfactory; however we did have some problems with the 2.0m tests. The reaction started so quickly as soon as we combined the calcium carbonate and the hydrochloric acid, that by the time that we had put the bung on the boiling tube, a lot of the gas had already escaped. If we were to perform the experiment again, we would consider using a tap funnel:
Another discrepancy that occurred during then experiment was the
mass of the calcium carbonate, when we measured it out, we
contained it in small plastic trays, when we added the powder to the
boiling tube, some of the powder stuck to the plastic trays and some
spilled over the side of the boiling tube, whilst these were small
amounts, it still affected our results. Another problem was getting the
bung on the boiling tube, the time it took varied between experiments
this could also be solved using a tap funnel. Despite these problems I
do think that the results prove my prediction and I am happy with
them, further experiments that could be carried out might include,
changing the mass of the calcium carbonate used or timing how long it
took for the reaction to finish with different concentrations as opposed
to timing for one minute.
