Using mole ratios of electrolytic products of water for analysis of household vinegar: An experiment for the undergraduate physical chemistry laboratory

摘要

A simple 3-h physical chemistry undergraduate experiment for the quantitative analysis of acetic acid in household vinegar is presented. The laboratory experiment combines titration concept with electrolysis and an application of the gas laws. A vinegar sample was placed in the cathode compartment of the electrolysis cell. Electrolysis of water generated OH -(aq) in the cathode compartment. Acetic acid in the vinegar sample was neutralized by electrolytically generated OH -(aq). Phenolphthalein was used as a visual indicator to detect the end point of the titration. The volume of O _2(g) produced at the anode was monitored. The amount of OH -(aq) produced at the cathode was determined from the volume of O _2(g) produced at the anode. The amount of acetic acid present in the sample was determined from the mole relationships between H ~+(aq), OH -(aq), and O _2(g). The concentration of acetic acid in household vinegar was determined to be 4.8%. The experimentally determined percentage of acetic acid was in agreement with the manufacturers label and the volumetric titration results. The electrolysis cell was directly powered by a 9 V battery. Preparation of an electrolysis cell, experimental procedure, and results of the electrolytic titration are presented.