· Surface area of the magnesium
If the magnesium had a bigger surface area each time the experiment was done, then the acid particles will have a bigger area to collide with, so more collisions will occur every second and the more collisions per second than the more successful collisions per second.
· Type of acid used
If you changed the type of acid then the rate of reaction would change. Hydrochloric, Sulphuric and Nitric acid all would produce a different rate of reaction, so if I do change the type of acid then all three kinds would produce a different set of results.
Key factor
I have chosen to use the concentration of the acid as my factor that I will change. I chose this because several different concentrations can be made up before the experiment by the lab technicians and they will be able to make them accurately.
There will be several different concentrations of acid, which will give me a wide range of results, which will be reliable and reproducible.
Prediction
My prediction is that the higher the concentration of the acid then the higher the rate of the reaction will be. I am saying this because of the collision theory. The higher the concentration of acid then the higher the number of acid particles present per 100cm3 of acid. This means that there will be more collisions per second, which means there will be more successful collisions per second, so the rate of reaction will increase.
If I double the concentration of the acid from 1M hydrochloric acid to 2M hydrochloric acid then I will expect to see the rate of the reaction double. This is because there are twice as many acid particles in 2M hydrochloric acid than in 1M hydrochloric acid, so there will be twice the amount of collisions per second and because there are twice the amount of collisions per second then there will be twice as many successful collisions per second, increasing the rate of reaction.
Fair Test
In order to keep my experiment a fair test I will have to make sure that I keep the following factors the same:
· Starting temperature of the acid
· Volume of acid used (cubic centimetres)
· Surface area of the magnesium
· Clean the magnesium with emery paper before experiment
· Length of magnesium
I will also have to make sure that the gas syringe is correctly connected and that it is placed quickly and tightly enough so that no hydrogen gas escapes.
The following factor that I will change is:
· The concentration of the acid
Preliminary work
The preliminary work that I will be conducting is to find out the optimum length of magnesium ribbon and the optimum volume of hydrochloric acid.
To do this I will be measuring out a volume of hydrochloric acid and a length of magnesium ribbon and reacting them together. If there is still some magnesium left over when it has stopped effervescing then I will have to increase the volume of hydrochloric acid.
If the reaction takes too long to finish then I will have to shorten the length of magnesium that I use, however if the reaction is too short then I will have to do the opposite and increase the length of magnesium that I use. The optimum rate that I am trying to find is a reaction that isn't too short but isn't too long, so I can get enough results to plot a good graph. I need to find the optimum volume of hydrochloric acid so that it is in excess after the reaction is over.
Apart from trying to find the optimum rate of reaction I also have to find out how to keep the temperature change down. This is because as the reaction is taking place the temperature will rise because the reaction is exothermic, and this could cause my results to be inaccurate as the temperature change will heat up the acid and give the acid particles more energy so they will move faster and collide with the magnesium with greater force causing more successful collisions per second.
Method
1. Put on safety goggles
2. Collect clamp stand, clamp and boss
3. Collect conical flask and measuring cylinder
4. Collect stop clock
5. Measure out 50 cm3 of 0.0M hydrochloric acid with the measuring cylinder
6. Pour hydrochloric acid into the conical flask
7. Collect thermometer
8. Measure the starting temperature of the hydrochloric acid
9. Measure 3cm of magnesium ribbon
10. Clean the surface of the magnesium with the sandpaper
11. Drop the magnesium into the conical flask
12. Quickly place the rubber bung into the conical flask
13. Start timing with the stop clock
14. Record the amount of gas evolved every 5 seconds for 15 seconds
15. Measure the temperature of the solution after the reaction is over and measure the temperature change
16. Repeat steps 5 to 12 changing the concentrations of the acid
17. Repeat steps 5 to 15 to make sure that my results are reliable and reproducible
Conclusion
My results table and graph show me that when I increase the concentration of the hydrochloric acid, the initial rate of reaction also increases.
Altogether I tested 5 different concentrations of hydrochloric acid. 0.0M, which was the lowest concentration of acid that I used, there was no reaction. 2.5M hydrochloric acid, which was the highest concentration that I used, produced the fasted rate of reaction. I repeated all 5 concentrations twice to be sure that they were reliable results and in all cases the higher the concentration the higher the rate of reaction. I had stated this in my prediction.
However I also stated in my prediction that if I doubled the concentration from 1M to 2M hydrochloric acid then the rate of reaction will also double. I have discovered that this is not the case.
Evaluation
Was I precise in my measurements?
I feel that I was precise and accurate in recording measurements.
I measured the acid accurately by measuring the acid when the bottom of the liquid meniscus just touched the line on the measuring cylinder.
Liquid Meniscus
Measuring cylinder
I accurately cut the magnesium ribbon to the nearest millimetre with the ruler provided.
I measured the starting and the end temperature accurately with a thermometer to the nearest .5OC.
I accurately measured the volume of gas evolved to the nearest .5cm3.
I accurately measure the time that had elapsed to the nearest second with the stop clock.
Did I take enough readings?
Not enough concentrations were used for a good graph. I should have used concentration 3M acid ought to have been done but it was not known then that it was necessary and required.
The results that I did collect were reliable as I repeated the experiments twice to obtain good average results. My results were not only reliable they were reproducible.
