Investigating Factors Affecting the Rate of Reaction.

        I then found out that the calcium carbonate powder was making the reaction too fast, and so I changed to marble chips made of calcium carbonate instead. This was successful, as it slowed the reaction down enough for me to measure.

        Once I had changed to marble chips, I decided to weigh the amount used, as 2 spatulas of calcium carbonate was not very accurate. I began by using 5g of marble chips, but this was too much. After testing 3.5g and 3g too, I settled on 2.5g of marble chips for my final investigation.

These are the results of my final pilot test, once I had made the reaction measurable, using 30cm3 of solution and 2.5g of marble chips. I will record my final results in a table like this one too.

These results appear to be accurate, and they fit my prediction, so I will use the same procedure, apparatus etc. as I used in my pilot test.

Apparatus List

1 x clamp

2 x beakers

1 x conical flask

1 x gas syringe

1 x syringe

1 x bung with delivery tubes

1 x stopclock

Marble chips

Water

Hydrochloric acid

1 x balance

I have chosen this apparatus as it is the easiest to use for this investigation, and it gives clear and accurate results. The gas syringe was the easiest way to measure the CO2 given off accurately, and the balance was accurate to 0.1g, which allowed me to measure the 2.5g of marble chips correctly.

Apparatus Setup

Procedure

Firstly I will set up the apparatus as shown in the diagram. Using a balance, I will weigh out 2.5g of marble chips, and the desired amount of acid and water solution using a syringe. I will put the solution into the conical flask, add the marble chips and quickly bung it, starting the stopclock at the same time. I will take a recording every 15 seconds for one minute. For safety, I will ensure I am wearing safety glasses to protect my eyes, wash my hands if I come into contact with acid and tie my hair back.

Fair Test

In order to carry out a fair test, I will keep everything the same except the concentration of the solution. Therefore the length of time I measure for, the amount of liquid, the equipment, the procedure and the amount of marble chips must remain the same.

Designing the Results Table

I will record my results in the same table as I recorded my pilot test results in as it was simple to use and an easy format.

Example

Additional Points

I have to repeat my measurements more than once to ensure accurate results. It is only possible to vary one factor at a time for this investigation, or I would not know which factor was affecting the rate of reaction.

Obtaining Evidence

Results for Investigation 1

Results for Investigation 2

Results for Investigation 3

Average Results Table

These are the averages for the results I got from my experiments.

In order to plot these points on my graph, I will need to find out the rate of reaction and the concentration percentage. These can be found through two simple equations.

Rate of Reaction = overall gas released

                                time

Concentration Percentage =        amount of acid used     x 2            

                                          total solution (30)

I can now use the following table to plot points on my graph. It shows only the overall gas given off, the rate of reaction and the concentration.

Analysing my results

I have drawn a graph to show the rate of reaction against the concentration, shown as a percentage of 2 due to the original acid used being 2 molecular. The graph is shown in appendix 1. It shows that as the concentration increases, so does the rate of reaction. This fits my earlier prediction. The results seem to fit the curve, as there do not appear to be any anomalies which do not fit onto the line of best fit. I could, however, use more frequent changes in concentration, e.g. measure every 2cm3 of acid to water instead of every 5cm3. This would give me a wider range of results, making it clearer to see any anomalies.

        I think the scientific theory to explain my results is the collision theory, as described in my prediction. This theory is that the rate of reaction depends on how often and how hard the reacting particles collide with each other. More collisions increase the rate of reaction. If the solution is made more concentrated, it means there are more particles of reactant molecules knocking about between the other molecules. This makes the collisions between the important particles more likely. If the particles are more likely to collide, then they are also more likely to react. Therefore, an increase in concentration causes an increase in reaction rate. As my graph has shown that increasing the concentration also increases the rate of reaction, this theory fits my prediction and results.

        I also noticed on my graph that when the concentration was 0.6, the rate of reaction was 0.4. When I doubled the concentration to 1.2, the rate of reaction was 0.85, which is just over double too, confirming that the rate of reaction is directly proportional to the concentration.

Evaluation

My results were very accurate as my graph shows a fitting line of best fit with no anomalies. Also, when I was finding the average results for the points to be plotted on the graph, I could include all of my results as there were no anomalies there either which might have affected the final results.

        There was nothing in my investigation that I found difficult or awkward to do. I chose to investigate the effect of concentration on rate of reaction rather than temperature as I thought it would be easier, as getting a solution to a particular temperature and maintaining it could be tricky. Therefore I found my method simple and easy to carry out. I think using the gas syringe ensured accurate results as it is a simple piece of equipment to use but produces quite detailed and accurate readings. It is definitely a better method than using a measuring cylinder, counting bubbles etc.

        I think my method and equipment ensured accurate results but if I was to try and get more accurate results I could use more frequent changes in concentration, e.g. measure every 2cm3 of acid to water instead of every 5cm3.  This would give me a wider range of results, making it clearer to see any anomalies.

        I think as my graph had a line of best fit with no anomalies and I did not notice any anomalies when finding the averages of my 3 investigations, my results are accurate enough to support a strong conclusion.

Conclusion

The higher the concentration, the faster the reaction rate.

Vickie Cannam 11C/Y