From our results, we calculated a random error of 2%. These errors are due to many
factors, but the main reason is inconsistency in pipetting the solutions. An error less
than 5% was acceptable for this experiment.
Other sources of errors are avoidable. The cuvette should be clean (we were careful
not to touch the transparent sides), and always placed in the spectrophotometer in the
same direction. Bubbles in the solution should be avoided since they also scatter light.
We removed small bubbles by tapping the cuvette on the lab bench. It is also not a
good idea to measure absorbances which are less than 0.01 or greater than 2, since
these values correspond to 99% and 1% transmittance respectively of the original
light beam. Most spectrophotometers have a sensitivity of this order, so the error in
measurement is large. We measured a series of concentrations, so we proceeded from
the lowest to the highest concentration. This minimises the error due to residual
solution left in the cuvette from the previous measurement. Ideally, the cuvette should
be cleaned between each measurement.