Dear Solomon,

You should use the following formula:

N1V1 = N2V2

Where N1 and V1 are the normality of sodium hydroxide and its volume and N2 and V2 are the normality of the acid contained in milk and volume of milk.

0.1 x 12.5 = 10 x N2;

Therefore the acidity of milk will be:

N2 = 0.125; 0.125 equivalent of acid per 1 liter; 125 mEq/Liter.

Hoping this will be helpful,

Rafik

                                               No of ml. of 0.1 N NaOH solutions

   Acidity                                  required for neutralization                x 0.009

(% Lactic acid) = ---------------------------------------------------------------------- x 100

                                                             Weight of sample

                               (Weight of sample = Volume of milk x specific gravity)

References:

IS : 1479 ( Part 1 ) – 1960 (Reaffirmed 2003)