What is Acid value?
Acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to
neutralize one gram of chemical substance. The acid number is a measure of the amount of carboxylic acid groups in a chemical compound such as a fatty acid. In a typical procedure, a known amount of sample dissolved in organic solvent is titrated
with a solution of potassium hydroxide with known concentration and with phenolphthalein as a color indicator.
The acid number is used to quantify the amount of acid present, for example in a sample of biodiesel. It is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic
constituents in 1 g of sample.
APPARATUS:-
Conical flask, burette, pipette, water bath
REAGENTS:-
0.1 N KOH, neutralized ethyl alcohol, phenolphthalein indicator
PROCEDURE:-
1. Weigh 0.2-0.5gms of sample in 250ml conical flask.
2. Add 50ml of neutralized ethyl alcohol.
3. Heat the mixture on a water bath to dissolve the sample.
4. Titrate the solution against 0.1N KOH using phenolphthalein indicator. The end point will be from colorless to pink.
CALCULATIONS:-
Acid value = A x N x 56.1
W
Where:- A – ml of 0.1N KOH consumed for sample.
N – Normality of
KOH
W – Weight in gms of
the sample.
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