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 I 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.
Preliminary work
I have done some experiments testing out the two acids. We have tested the two reactions to see how much CO2 is given if we counted the amount of bubbles in one minute, as at the start as we didn’t need to be deadly accurate. This will give us suitable information for a range.
Hydrochloric acid (HCL)
Little chips
Medium chips
Large chips
Sulphuric acid (H2SO4)
Little chips
Medium chips
Large chips
From my preliminary work I have decided to use hydrochloric acid as it reacts for a suitable amount of time in order for us to make reliable results. The hydrochloric makes far more CO2 than sulphuric as it only reacts for about 15 seconds creating a very little amount of bubbles; this is because the calcium sulphate forms a layer over the CaCO3, which stops the reaction making the CaCO3 impermeable.
So therefore I have chosen to use Hydrochloric acid with medium size chips, as the results would be at a very suitable range with these two variables.
The reaction I am doing is: CaCO3 + 2HCL → CaCl2 + CO2 +H2O
Method
I will be collecting over water in the following set-up of my experiment:
- I will set up my experiment as above.
- I will put 40ml of 2 molar HCL into the side arm flask.
- I will measure out 2g (0.4 leverage either way) of marble chips medium sized.
- I will put the marble chips into the side arm flask and start the timer.
-
Every 30secs I will take a reading of the volume of CO2 given off and record it in my table.
- Restart experiment with different molar of acid E.g. 1.5M, 1.0M, O.5M and 0M.
- Repeat all molars
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 40cm3 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.
From my prelim work it would be suitable to take a reading every 30 secs and gain a suitable graph and firm conclusions.
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)
· size 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.
Observations
Molars are as follows: 2M = 40ml of acid
1.5M = 30ml acid- 10ml of water
1.0M = 20ml each
0.5M = 10 ml of acid- 30 ml of water
0.0M = 40ml of water
Averages
To find Average CO2 = add 2 results
2
Trends and patterns
From my graph all molars present a straight line this would indicate a doubling of the rate of reaction for all molars but because the straight line shows as every 30-second reading it doubles. A straight line shows a constant increase and in this case it is doubling.
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. 2.0M 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.
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 the case as see below it approximately doubles from 0.31 to 0.66.
As you can see from this table as the concentration doubles then the rate of reaction approximately doubles.
I therefore conclude that:
1. The initial rate of reaction increase as the concentration of the acid increases
2. There is a twofold increase in the rate of reaction as the concentration doubles
Evaluation
The method I used was good but it could have been better the results could have been made more accurate and reliable by making sure the bung didn’t stick to the sides after lots of testing and therefore letting gas out.
Improvements to my experiment are that I could stop the bung sticking by applying a thin coating of Vaseline to it. Also we blocked the pip by accident this aloud an anomalous result but we re-done the test and get rid of the anomalous result. Any anomalous results were rid off by further tests.
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 touched the exact amount I needed.
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. The results I produced were reliable enough to base my conclusions the experiment was successful as a whole but had errors the experiment could be done again and my conclusions would still be the same although the figures would be more accurate.
Further work
I could use sulphuric acid. This is a dibasic acid and its molecular build-up is H2SO4 and hydrochloric acid is 2HCL, because of this I would obtain different results. I could also use phosphoric acid, which is a tribasic acid, and its molecular build-up is H3PO4, I would also obtain different results if I used this type of acid. Nitric acid is a monobasic acid but its molecular build-up is HNO3, which is very similar to the molecular build-up of hydrochloric acid so the results that I would obtain from using this acid would be similar to the ones I already have, so I would not use this for any further experiments. The reason I could use a different type of acid for any further work is to find if the is a difference between them if their molecular build up is different.
I also could improve this experiment by making sure the surface area was the same. my surface areas where the same approximately but I could have made this more accurate by using cubic chips where the surface areas where known. This way it will make the example eevn more accurate than it was.
Bibliography
I obtained most of the information that I needed for my experiment form my teacher and exercise book. I also obtained information from several science textbooks and computer encyclopaedias. I obtained a small amount of information from the Internet