Introduction
The saponification value (SV) is a measure of the amount of alkali (usually potassium hydroxide, KOH) required to hydrolyze (saponify) one gram of fat or oil. It reflects the average molecular weight (or chain length) of the fatty acids present in the fat or oil. The saponification value is inversely proportional to the molecular weight of the fatty acids: shorter chain fatty acids yield a higher saponification value, while longer chain fatty acids yield a lower saponification value.
Principle:
When an ester (fat or oil) undergoes hydrolysis in the presence of a strong base such as KOH, it produces glycerol and soap (the salts of fatty acids). In this experiment, an excess of alcoholic KOH is added to a known quantity of oil or fat and heated to ensure complete saponification. After the reaction, the unreacted KOH is titrated against a standard acid (hydrochloric acid, HCl) to determine how much of the KOH was consumed in the saponification reaction. The difference between the added and the titrated KOH gives the amount of KOH that reacted with the oil/fat.
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Saponification Reaction:
Fat(or/Oil)+KOH =Glycerol +soap(Potassium salt of fatty acid)
Titration Reaction (between unreacted KOH and HCl):
KOH(unreacted)+HCl = KCl + H2O