Finding our how much acid there is in a solution.

The measurements I took from the burette were only to two decimal places as this was all my equipment would allow. I think this delivers a good degree of accuracy but could be more accurate with more specialised equipment.

Errors almost certainly have occurred in my results, mainly human error but some also by errors in my procedure, technique and equipment have caused these. My reading of the meniscus in the burette could have caused some of the error, if I was not always careful. I could accurately read my burette to two decimal places, with the final place only being a 0 or a 5 as the burette is only marked at 0.1 cm3 intervals, this brings my degree of accuracy down. Even thought I rinsed all my apparatus with distilled water before use and the burette with sulphuric acid, contamination may have occurred which would have affected my results. The amount of sulphuric acid I used in each titration was determined by when I saw a colour change in the indicator in the conical flask. It is possible that I could have missed the exact moment when this occurred and used too much acid. If I were to repeat this experiment in perfect conditions I would devise a method using a form of 'light detector', which would give me a second opinion of when a colour change had occurred, so I don't use too much acid in my titrations.

Percentage error can be calculated by:

Precision error * 100

Actual reading

Errors caused by equipment and glassware:

? Volumetric flask when filled correctly has a precision error of 0.2 cm3 so has a percentage error of 0.08%

? All burette readings should include 2 decimal places in which the second figure should be a 0 or 5. An error of one drop gives an error of 0.2% for each reading.

? A pipette delivers a percentage error of 0.063 cm3 or 0.24%

? A digital balance gives readings up to two decimal places this means the actual reading could be +/- 0.005g of the reading took.

(0.005*100/1.06= 0.47) so the digital balance delivers a percentage error of 0.47%.

It is important to repeat a titration several times to check that the results are reliable. After calculating the average titre, we should correct the value to one decimal place; in our case the average titre was 11.0 cm3

Quantity measured

Percentage error

Mass of sodium carbonate weighed on digital balance

0.47%

00 cm3 solution made up in volumetric flask

0.08%

0 cm3 Solution delivered by pipette

0.24%

Average titre delivered by burette

0.2%

These are errors caused by limitation of the procedure and equipment. Human error is the main source of error; a value cannot be put on this error. Since I carried out the experiment 3 times, the percentage error caused by human error was decreased. Good technique in titration is a major way of reducing human error and errors not caused by equipment:

? Solution in volumetric flask needs through mixing.

? Burette and pipette should be washed out with the solution used.

? The conical flasks should be thoroughly washed out with distilled water between titrations.

? The end-point of a titration can only be determined accurately if the solution from the burette is added drop by drop, with swirling, as the end-point is reached.

? When we use an indicator in the titration only the minimum of drops should be added each time.

Since the errors caused by the equipment are not too great, I do not think they had a great effect on my results. To reduce the error they did cause I would have to use more specialised and accurate equipment, even so, there will always be a degree of error. Human error is by far the greatest cause of error as mentioned before; I do believe it is great enough to affect my results. I believe they made my titres on average greater.

If I were to repeat this experiment in order to reduce errors I would have to carry out the same experiment a number of times or devise a method that removes the majority of human error. I could try to do this by even letting my equipment display the measurements digitally, or detect the colour change more accurately, for example using a light detector and beam of light through the conical flask. I could use a balance with a display of more than 2 decimal places. I could test that the sodium carbonate solution was correct before I carried on, I could also test the acid for inaccuracies there. I could practice my titration techniques in order to reduce human error in measuring out each substance correctly. My reading of the burette would become more accurate with practise. I could even use an indicator with a more distinctive colour change. A detailed new and improved way of carrying out this experiment would reduce the percentage error of my results by reducing the error caused by the main cause of error, human error and make the results obtained more accurate and reliable.

Overall I do not believe my results to be completely inaccurate and I think they are reliable enough for what we are trying to discover in this experiment. I would have to increase the repetitions of my experiment to get a more reliable and accurate result. As previously stated there are ways and improvements in my procedure and technique to make my results as accurate as possible.

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