1. Abstract
This laboratory experiment was done to determine the concentration of a mixture of a
weak monoprotic acid – Acetic acid (CH3COOH) and a strong monoprotic acid –
Hydrochloric acid (HCl) using potentiometry. The experiment was carried out two days
in a two-week period. On day 1, a prepared solution of sodium hydroxide was
standardised with the acid mixture to find the end points of neutralisation in a rough
titration and a graph of pH versus NaOH volume was plotted. Using the rough graph as a
guide, the mixture was carefully (drop-wise additions of NaOH) titrated and a more
accurate graph plotted. The standardisation of NaOH with potassium hydrogen phthalate
showed the average concentration to be 0.0971M. Following the titration, a more
statistical analysis was done to determine the concentrations of each acid in the mixture.
The concentrations were calculated based on the volume at which the indicator colour
changes for both days, a first derivative plot, a second derivative plot and a Gran plot.
The concentrations calculated for the weak acid - CH3COOH by first derivative, second
derivative and Gran plots respectively are 0.087M, 0.087M and 0.061M. The expected
concentration was within the 0.05M range. The concentrations calculated for the strong
acid - HCl by first derivative, second derivative and Gran plots respectively are 0.073M,
0.074M and 0.075M. The expected concentration was within the 0.10M range.
1
