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)
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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 %.