B.S (Hons.) 3rd Semester Organic Chemistry Practicals

BS (Hons) 2nd Semester Organic Chemistry Practical Manual

ExperimentTitle:Determination of saponification value of a fat or oil.TheorySaponificatiin is the process by which the fatty acids in the glycerides of oil are hydrolysed by an alkali. Each mole of triglyceride uses three moles of KOH for saponification as per the following equation:

CH2OCOR+CH2OH

CHOCOR3KOH+ 3RCOOK

CHOH

CH2OCOR

CH2OH

TriglycerideGlycerolPotassium salt of

fatty acid (Soap)

Saponification value is the amount (mg) of the alkali required to saponify 1 g of an oil or fat. This value is useful for comparative study of the fatty acid chain length in oils.

A known quantity of the oil is refluxed with a known excess of alcoholic KOH. After Saponification, the remaining KOH is estimated by titrating it against a standard acid.

Materials1. Alcoholic KOH: Dissolve KOH (40 g) in distilled alcohol (1 litre), keeping the temperature below 15oC while the alkali is being dissolved (1N).

2. 0.5N HCl, accurately standardized.

3. Phenolphthalein indicator: 1% in 95% ethanol 4. Air condensers

Procedure1. Weigh completely dry liquid sample (4.5 g) into a flask.

2. Add alcoholic KOH (50 ml) slowly from the burette into the flask.

3. Simultaneously, process another flask in the same way without adding the sample, connect air condensers to the flask and boil the contents gently on steam bath for about an hour. 4. Allow the contents to cool at the room temperature and rinse the inside of the condensers with a little distilled water and then remove the condensers. 5. Titrate the solutions against 0.5N HCl using phenolphthalein as indicator. 6. The end point is the just appearance of pink colour (pink to just colorless). 7. From the difference between the titration values of the blank flask and the flask containing the oil, the amount of KOH in mg (saponification value) that has been used for 1g of the oil, can be calculated.

CalculatonsSaponification value = 28.05 (titre value of blank Titre value of sample)

Weight of sample (g)

1Dr. Muhammad Aslam

Assistant Professor-Chemistry

University of Education, Township Campus, Lahore.