Saponification is the process by which the fatty acids in the glycerides of the oil are hydrolyzed by an alkali. Saponification value is the amount (mg) of alkali required to saponify a definite quantity (1g) of an oil or fat. This value is useful for a comparative study of the fatty acid chain length in oils.
A known quantity of oil is refluxed with an excess amount of alcoholic KOH. After saponification, the remaining KOH is estimated by titrating it against a standard acid.
» Hydrochloric acid 0.5N, accurately standardized.
» Alcoholic KOH
– Dissolve 40g KOH in one liter of distilled alcohol keeping the temperature below 15.5o
C while the alkaline is being dissolved. This solution should remain clear.
» Phenolphthalein Indicator
– 1% in 95% alcohol.
» Air Condenser.
||Melt the sample if it is not already liquid and filter through paper to remove any impurities and the last traces of moisture. The sample must be completely moisture-free.
||Weigh 4-5g sample into the flask. Add 50mL of alcoholic KOH from burette by allowing it to drain for a definite period of time.
||Prepare a blank also by taking only 50mL of alcoholic KOH allowing it to drain at the same duration of time.
||Connect air condenser to the flasks and boil them gently for about 1h.
||After the flask and condenser get cooled, rinse down the inside of the condenser with a little distilled H2O and then remove the condenser.
||Add about 1mL of indicator and titrate against 0.5N HCl until the pink color just disappears.
|Saponification value =
||28.05 x (titer value of blank – titer value of sample)
Weight of sample (g)
1. Alcohol is inflammable. Use electrical heating.
2. Alcohol should not get dried up during saponification. Effective cooling of alcohol vapor is essential.
3. Clarity and homogeneity of the test solution are indicators of complete saponification.
1. William Horowitz (ed
) (1975) Official Methods of Analysis of AOAC
Association of Official Analytical Chemists Washington 12th
Ed p 490.