2.67 / 106 = 0.0251 mols in 250 cm3
So the concentration of the Na2CO3 solution was: 0.1004 mol dm-3.
So in the 25cm3 of Na2CO3 solution I used, there were:
0.0251 / 10 = 0.00251 mols.
The equation shows how 1 mol of Na2CO3 reacts with 1 mol of H2SO4, so 0.00251 mols of Na2CO3 reacts with 0.00251 mol of H2SO4. So in the 25.92 cm3 of acid I reacted with the Na2CO3 solution, there are 0.00251 mols. So the concentration of the acid is:
( 0.00251 / 25.92 ) x 1000 = 0.0968 mol dm-3
So the concentration of the acid is 0.0968 mol dm-3.
Evaluation:
There may have been some limiting factors during the experiment which may have affected the results. The first of these may have been the scales, it is possible that when I was weighing out my Na2CO3 crystals, I spilt some on the scales themselves and this would mean that the weight that I calculated was inaccurate and so the above calculations would be inaccurate too.
It is then possible that when I was dissolving the Na2CO3 crystals in distilled water in the beaker, I may have spilt a few drops on the floor or left some on the glass rod or in the bottom of the beaker when I poured it into the graduated flask. This would mean that some of the Na2CO3 would have been lost, which would in turn affect my results.
Another possible source of possible error is when it comes to reading the burette. Each time I took a reading, I lowered the burette to eye level and held a piece of white paper up behind it. It is however still possible that I accidentally misread one of the readings, which would again affect my results, as my calculations would all be incorrect.
One of the most important steps in the procedure, and the one where it is most easy to make mistakes is the stage at which you stop letting the acid through the burette because the solution is neutral. The grey colour is present for such a shot period of time that it is easily overshot or under estimated. I may have done this several times during the experiment.
The most important stages in the practical which ensure that my data is correct and reliable are the weighing stage, and the stage in which the solution becomes neutral, as getting these readings wrong could easily interfere with the experiment. It is also very important to measure out exactly 25cm3 of the Na2CO3 solution and to read the burette accurately.
There is a level of uncertainty on all measurements that I make because the are subject to human error. The percentage errors for the main different parts of the experiment are as follows (using the equation: error x 100 / reading):
Balance: 0.18 %
Volumetric Flask: 0.08%
Burette: 0.19%
Pipette: 0.24%
As you can see, the percentage errors here are very small, but, to take the example of the pipette, the volume error is 0.06cm3 – which means that if I fill up to 25cm3 then the real value could be between 24.94cm3 and 25.06cm3. This could make a difference in my calculations. One way to help minimise the percentage error is by using larges quantities of substances, as this would decrease the amount by which you can go wrong.
I feel that I was fairly accurate in my procedure and I am happy with how it went and I believe my result to be accurate.
