Dissolve 0.2884gm of sodium decyl sulphate, calculated about the substance at 105˚C for 2 hrs, in sufficient water to produce 1000ml. Standardise the solution in the following manner.
STANDARDISATION (TRIPLICATE)
To 50 ml of the solution add 15 ml of chloroform, 10 ml of sulphuric acid and 1 ml of dimethyl yellow–orate blue solution. Titrate with 0.004M benzethonium chloride, shaking vigorously and allowing the layer to separate after each addition until the chloroform layer acquires a permanent clear green colour.
Each 1ml of 0.004M benzethonium chloride is equivalent to 0.001154gm of C12H25NaO4S.
Calculation
Molarity = ----------------------
V1
Where M2 = molarity of 0.004M benzethonium chloride solution.
V2 = volume of 0.004Mbenzethonium chloride consumed in
ml
V1 = volume of 0.004M sodium lauryl sulphate taken in ml.
ACCEPTANCE CRITERIA
1) The accuracy of the solution should be within ± 10% of the theoretical concentration.
2) RSD* of the triplicate results of standardization / re-standardization should not be more than 0.2 %.