Determination of Acid value in oil

Principle: 

The acid value is determined by directly titrating the oil/fat in an alcoholic medium against standard potassium hydroxide/sodium hydroxide. Acid value is a measure of hydrolytic rancidity present in the sample.

Definition: 

Acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide  (KOH) in  milligrams  that is  required to  neutralize free fatty acids present in  one  gram  of  fat.The  Acidity  of  an oil is expressed  as  oleic acid and  is  measured  by adding neutralized  alcohol  to  the  oil  sample and  titrating  it against 0.1 N sodium hydroxide solution under hot conditions.

Apparatus:

Conical flasks

Burette

Pipette

Reagent:

a. 0.1N Std. Sodium Hydroxide solution

b. Rectified spirit

c. 1% phenolphthalein indicator

Procedure:

Weigh accurately about 5-10g. of oil sample in a conical flask. Add 50 ml to 100 ml of freshly neutralized hot rectified spirit. Add 1 ml of phenolphthalein indicator solution. Boil the mixture for about 5 minutes and titrate while as hot as possible with Std. 0.1N NaOH solution, shaking vigorously during titration.

Calculation:

Acid Value= 56.1 x Vx N/W

Where,

V= Volume in ml of Std. Sodium hydroxide solution. 

N= Normality of Std. Sodium hydroxide solution

W= Weight in gram of sample taken for the test.