Preparation and standardization of 0.02 M Disodium Edetate BP Volumetric Solution
Accurately weigh and dissolve 7.444 g of Disodium edetate in sufficient water to produce 1000 ml.
Accurately weigh and dissolve 0.100 g of Zinc, in granules, in 4 ml of 7 M Hydrochloric acid and add 0.1 ml of Bromine water. Boil to remove excess bromine, cool and dilute to 100 ml with water. Dilute 25 ml of this solution to 200 ml with water. Add about 50 mg of Xylenol orange triturate and Hexamine until the solution becomes violet-pink. Add 2 g of Hexamine in excess. Titrate with 0.02 M Disodium edetate VS until the violet-pink colour changes to yellow.
Each ml of 0.02 M Disodium edetate VS is equivalent to 1.308 mg of Zn.
Molarity (M) = [0.02 x weight of Zinc (in g) x 25]/[ Titration reading (in ml) x 100 x 0.001308]
Limit: 0.02 M ± 5 % [ 0.019 M – 0.021 M ]
3. PREPARATION OF INDICATORS / REAGENTS:
a. 7 M Hydrochloric acid:
Dilute 59.5 ml of Hydrochloric acid to 100 ml with water.
b Bromine water:
A saturated solution obtained by shaking occasionally during 24 hours 3 ml of Bromine with 100 ml of water and allowing to separate.
Store the solution over an excess of Bromine, protected form light.
c. Xylenol orange triturate:
Triturate 1 mg of Xylenol orange with 99 mg of Potassium nitrate.
It should comply with the following test:
Sensitivity: Add 50 mg to a mixture of 50 ml of water, 1 ml of 2 M Acetic acid and 0.05 ml of Lead nitrate solution. Add sufficient Hexamine to change the colour from yellow to violet-red, and add 0.1 ml of 0.1 M Disodium edetate VS. The colour change to yellow.
d. Lead nitrate soluition:
A 3.3 % w/v solution of Lead (II) nitrate.
4. STORAGE CONDITION:
Store in a glass-stoppered bottles.