21. Standard Solutions and Titratable Acidity

The titratable acidity assay in this laboratory exercise is one of many types of chemical analyses in which a constituent is titrated with a standard solution of known strength to an indicator endpoint. From the volume and concentration of standard solution used in the titration, and the sample size, the concentration of the constituent in the sample can be calculated. The assay for titratable acidity is a volumetric method that uses a standard solution of sodium hydroxide which reacts with the organic acids present in the sample, titrating to a phenolphthalein or pH endpoint. The normality of the sodium hydroxide solution, the volume used, and the volume of the test sample are used to calculate titratable acidity, expressing it in terms of the predominant acid present in the sample. In this laboratory exercise, the standard acid, potassium acid phthalate, is used to determine the exact normality of the standard sodium hydroxide that is then used to determine the titratable acidity of food products.