Definition of Saponification Value- The number of milligrams of potassium hydroxide required to saponify completely one gram of the oil or fat.
Principle: The oil sample is saponified by refluxing with a known excess of alcoholic potassium hydroxide solution. The alkali required for saponification is determined by titrating the excess potassium hydroxide with standard hydrochloric acid. The saponification value is an index of mean molecular weight of the fatty acids of glycerides comprising a fat. Lower the saponification value, larger the molecular weight of fatty acids in the glycerides and vice-versa
Apparatus:
Flat bottom flask .
250 ml, Reflux condenser,
Water bath
Reagents:
Alcoholic Potassium hydroxide solution : Dissolve 35 to 40 g of potassium hydroxide in 20 ml of distilled water, and add sufficient aldehyde-free rectified spirit ( conforming to IS:323-1959 Specification for Rectified Spirit (Revised}]to make up to 1000ml. Allow to stand overnight, decant the clear liquid and keep in a bottle closed tight with a cork or rubber stopper.
Rectified spirit Phenolphthalein indicator 1 % Hydrochloric acid. 0.5 N
Procedure:
Weigh about 1.5g to 2.0g of the sample into a 250 ml flat bottom flask.Add 25 ml of approximately 0.7 N alcoholic KOH. Connect the reflux condenser to the flask. Boil the contents in the flask on the boiling water bath gently and steadily for 1 hr. Ensure the saponification by absence of any oily matter and appearance of clear solution. After cooling wash down the condenser with 10 ml of neutralized Ethyl alcohol. Carry out the blank at the same time. Titrate with std. 0.5 N HCL using 1 ml phenolphthalein indicator. Prepare and conduct a blank determination at the same time.
Calculation:
Saponification Value= 56.1 X (B- S) x N/W
Where,
B= Volume in ml of std. HCL acid required for the blank
S= Volume in ml of std. HCL acid required for the sample
N= Normality of std. HCL acid
W= Weight in grams of the sample taken for the test
No comments:
Post a Comment