Page 39 - Pharmaceutical analytical chemistry |

insoluble in water e.g. benzoic or salicylic acids, it is dissolved in
neutralized alcohol. Substances which contain an imido hydrogen and
acid salts are sufficiently acidic to be titrated with standard alkali.
Acid value of oils
Acid value is the number of milligrams of KOH required to neutralize the
free fatty acids in 1 g of the substance. It is a measure of the degree of
hydrolysis of oil or fat. It is also considered to be a test of freshness or
edibility of the sample. It is done by dissolving a certain weight of the
substance examined in 1 : 1 ethanol : ether followed by titration with
0.1 M KOH using phenolphthalein as indicator.

4) Determination of esters
This can be done through saponification and back titration of excess of
base with standard acid using phenolphthalein as indicator.
Saponification value of oils
Saponification value is the number of milligrams of KOH required to
neutralize the free acids and to saponify the esters in 1 g of the substance.
It is inversely proportional to the mean molecular weight of the fatty
acids. It also detects the adulteration with paraffin oil. A certain weight of
the substance to be examined is refluxed with a known volume of 0.5 M
ethanolic for an hour. The excess alkali is titrated with 0.5 M HCl using
phenolphthalein as indicator (a blank experiment should be carried out).

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