Measure out 25cm3 of 0.1mol/dm3 sodium carbonate solution using a 25cm3 pipette and pour into a 250cm3 conical flask. Fill the burette with 50cm3 of sulphuric acid so that the level reads 0 at the top of the burette. Ensure both the chamber at the bottom of the burette has been run through with acid as air bubbles can occur, and that the valve is closed so no acid escapes. Clamp the burette to the stand but make certain the tip of the burette is just slightly lower than the height of the conical flask. Add 2-3 drops of methyl orange to the conical flask containing the sodium carbonate solution. This indicates well between a strong acid and a weak alkali. Therefore we can easily determine when the solution reaches a weak alkali after a certain amount of acid is added. Place the conical flask under the burette so when the valve is opened the acid flows into the conical flask. Keep the valve open until the solution in the conical flask turns from orange to a skin coloured pink. This is the point of titration so record the amount of acid needed to reach this point. Repeat this procedure a number of times to get a set of similar results, an average can then be taken and any anomalous results can be identified.
Certain precautions must be taken to ensure both a safe and accurate experiment. Firstly all readings must be taken as accurately ensuring eye level is in line with top of liquid and the slight trough is in line with the measurements on the piece of apparatus. Care must also be taken over pouring the sulphuric acid into the burette as it only has a small opening. Sulphuric acid is irritating to the skin. Wear and apron and goggles in order that the solutions do not stain clothes, or get into the eyes. When using the scales ensure there is nothing effecting the result, even someone leaning on the bench could cause an effect, the digital scales are very sensitive. Whilst the conical flask is under the burette swirl the liquid as the acid is added this will spread the liquid around and ensure a more accurate titration point can be found.
Results:
From the above data we are able to calculate the morality of the acid.
H2SO4 (aq) + Na2CO3 (aq) → Na2SO4 (aq) + H2O (l) + CO2 (g)
1mol 1mol 1mol 1mol 1 mol
12.78cm of ?m H2SO4 solution + 25cm of 0.1m Na2CO3 solution = titration
Amount of mols of Na2CO3 used:
0.1/1000 = number of mols in 1cm3 of Na2CO3 solution = 0.0001m
0.01x25 = number of mols in 25cm3 of Na2CO3 solution = 0.0025m
Morality of sulphuric acid solution:
Therefore 12.78cm3 of H2SO4 solution = 0.0025m
0.0025/12.78 = number of mols in 1cm3 of H2SO4 solution = 0.000197 (3sf)
0.000197x1000 = the morality of solution (number of moles in 1000cm3) = 0.197 mol/dm3 (3sf) solution
From taking the average of my results I have calculated that the morality of the sulphuric acid is 0.197m/dm3. However, at the beginning of the experiment I was told that the morality would lie between 0.05 and 0.15m/dm3. Therefore I believe that a small fault in the experiment resulted in me calculating the morality higher than previously expected. This could have been caused by a number of inaccuracies, firstly I could have made my sodium carbonate solution too weak. Some of the solid sodium carbonate may have been blown away off the paper. This would result in the morality slightly lower and therefore seemingly increasing the morality of the acid. The judgement of the colour may have also caused a problem, as I had seen no preordained colour I could have inaccurately judged when the colour turned from orange to skin pink.
However I have come to the conclusion that the morality of the H2SO4 solution is higher than 0.1 and likely to be around the 0.15 area. I worked out the morality of the Na2CO3 solution earlier in the plan to show how we came to find out that 2.65g were needed to produce the 0.1m solution.
The results seem to be slightly lower than they should have been however there is one particular result that stands out as being particularly low, this is the 12.50cm3 result. I would consider this an anomalous result, as it doesn’t fit with rest of the results gained. In my conclusion I have already outlined how the morality came to be high than what was expected. This could have been due to some error when using the measuring equipment. Below are the calculations to find percentage error for each set of apparatus as well as the total percentage error:
Scales:
0.005 maximum error on reading scales, therefore the percentage error = maximum error / amount of substance weighed x 100 = 0.05 / 3.14 x 100 = 1.59%
Burette:
0.5 maximum error on reading burette, therefore the percentage error = maximum error / amount of substance measured x 100 = 1.0 / 50 x 100 = 1%
Pipette:
0.5 maximum error on reading pipette, therefore the percentage error = maximum error / amount of substance measured x 100 = 0.5 / 25 x 100 = 2%
From this information we are able to say that the maximum % error for the whole experiment = 4.59% If we look at this information as well as the possibility of misjudgement of the colour of the indicator there is a high possibility that the results are not going to be perfect. The inaccurate use of the measuring instruments could have caused me to use a slightly wrong morality of sodium carbonate solution as well as the possibility of the 1% error on the burette could have consequented in the results being as they were, slightly low. All these possibilities are going to effect the results, one slight wrong measurement for example of the solid sodium carbonate can effect the rest of the results throughout the experiment.
A number of different procedures could have been undertaken to ensure the most accurate results possible. Firstly it is imperative the measurements of liquids is done accurately. If possible, use small measuring apparatus this reduces the percentage error significantly. Then it is possible to transfer this into the larger container. The best idea however is to use a control colour so that it is possible to ensure the results all have the same pH reading. If possible use a control that you know is pH neutral then add the methyl orange and compare the results from the experiment to this control. Also by making larger quantities of the sodium carbonate solution there is a reduction in the percentage error, as a slight misjudgement has less effect the more substance and solution is being used. Instead of using the same solution of sodium carbonate for each repeat, re-make the solution, this will eliminate the possibility of the entire set of results be anomalous or inaccurate. It will provide a more accurate average at the end of the experiment than if you use the same solution throughout.
By using all the outlines above the results gained are more likely to be accurate and therefore it is possible to come to a stronger and more accurate conclusion. After taking on the precautions outlined after hindsight of the experiment each result will be more accurate, by in a way starting all over again after each repeat minimises the possibilities of a whole set of anomalous results.