The percentage error = error x 100 = 0.05 x 100
Reading 25 =0.2%
This is also low, meaning that the equipment has high accuracy.
Beakers:
The beakers are useful for measuring broad volumes of a solution. This is not very accurate but can give an approximate volume. I used it to measure the volume of water because the volume of water needed was approximate.
Conical flask:
These are good for titrations as they have a narrow neck (enough to fit in the burette tip, without breaking it when swirling), but broad base. This is particularly useful as the narrow neck prevents spillage when swirling and the broad base makes the solution and end-point easy to see.
Weighing balance:
A two place weighing balance has an error to 0.01g. Using it to measure a mass of 5g will have percentage error:
The percentage error = error x 100 = 0.01 x 100
Reading 5 =0.2%
This is low and has high degree of accuracy.
Apart from the errors and uncertainties related to the precision of the equipments used, procedural error may arise from practical techniques. This would include:
· Not mixing the solution in the volumetric flask thoroughly would make the solution have uneven concentration through out. Some areas would be more concentrated than others. A lower concentration would use less volume from the burette and this would make my result lower. A higher concentration would use more burette solution and would make my result higher.
· Not washing the burette and pipette with the solutions they are to contain before titrating can be a source of error as other substances may be present in the equipment. This can affect the concentrations of the solution, hence the volume of the titre used. The substances that will increase the value of the titre will make my result higher and the substances that will reduce the value of the titre will make my result lower.
· The conical flask needs to be thoroughly rinsed with distilled water in between titrations. This will remove any solution from the previous titration and not affect the concentration of the solution in which it is to contain, as the concentration of the solution is already known.
· Using a white tile makes it easy to read off the volumes from the burette. As the sulphuric acid is aqueous and transparent, so is the burette. This makes it difficult to read the volume and can affect the degree of accuracy in which the volume is read to. A lower volume gives a lower result.
The mass of sodium carbonate (between 1.33-3.98g) I used in making the standard solution of sodium carbonate was ideal because it was calculated theoretically taking into consideration the given concentration of sulphuric acid (between 0.05-0.15moldm 3).
The volume of sodium carbonate used in the titration (25cm 3) was appropriate because using a 25cm 3 pipette gives more accurate and reliable result than using a pipette with a greater volume capacity. Using a pipette of volume less than 25cm 3 would not make available enough solution for the titration and I would be working with very small values that can cause errors. The 25cm 3 pipette I used is not too small or too big, it is just reliable. Moreover, this is used in most standard titrations.
Making the solution of sodium carbonate to a volume of 250cm 3 in a volumetric flask made available enough solution in case I overshoot pass the end-point and need to repeat the titration. This also ensures that there is enough solution to repeat titrations so that different values of titre will be collected and the average of them taken. This ensures accuracy.
Since random errors affect reproducibility, they influence both precision and accuracy. Common random errors include titration errors, proper draining of buret, removing last drop from tip, and judging the correct color at the end point, weighing errors, judging the level of liquid in volumetric glassware, and parallax error in reading instruments and volumetric glassware.
Titration Errors with Acid/Base Indicators
a. Systematic error (determinate error):
i. Any error that affects the accuracy of the results (consistently low or high)
ii. pH at color change doesn't match pH at equivalence point
b. Random error (indeterminate error):
i. Causes data to be scattered symmetrically around the mean or true value
ii. Limitations on eye as analytical instrument
iii. Depends on
(b) concn of indicator
(c) eye sensitivity to two colors
