Question

calibration curve of KMnO4 y = 0.2425x -0.103 R2 = 0.8114. ABSORBANCE AT 525 0.5 2.5 3 3.5 1 1.5 2 CONCENTRATION (M)

• Write a short summary of conclusions on the linearity and whether your results are consistent with Beer’s Law relationship. If not, what could be the possible reasons for errors andhow would you improve your experimental process? (even if you had accurate values, comment from the perspective of a different student who might not get good results

Answer 1

Beer's law states that

A $\propto$ c where A is absorption and c is the concentration of the solution. So absorbance and concentration have a linear relationship according to Beers Law and they satisfy a y = m*x type of straight line i.e. a straight line with zero intercept. Now if we look into the experimental data and fitted line we can see that the fitted line has an equation y = 0.2425x-0.103. This is inconsistent with Beer's law as the intercept should have been zero. Moreover none of the experimental points are on the fitted line which is evident from the R² value of 0.8114. R² measures the goodness of the fit and is best when nearly equal to 1. So evidently there are many errors associated with the experiment.

The major source of error in a Beer's law experiment arises from concentration. Beer's law is only valid for low concentration ranges, not for high concentrations. So if the experiment was performed at lower concentrations then a better data set could have been obtained. Other sources of experimental errors can arise from improper cleaning of the cuvette before measurement. If some other material is present in the cuvette or sample from the one data point is not cleaned properly then light can be absorbed by them which will impose error. So each time cuvette needs to be cleaned properly.