Preparation and standardization of 0.05 M Disodium Edetate BP Volumetric Solution

1.  PREPARATION:

Accurately weigh and dissolve 18.6 g of Disodium edetate in sufficient water to produce 1000 ml with water.

2. STANDARDISATION:

Accurately weigh and dissolve 0.060 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 the Disodium edetate solution until the violet-pink colour changes to yellow.

Each ml of 0.05 M Disodium edetate VS is equivalent to 3.269 mg of Zn.

Calculation:

Molarity (M) = [0.05 x weight of Zinc (in g)]/[ Titration reading (in ml) x 0.003269]                                   

Limit: 0.05 M ± 5 % (0.0475 M – 0.0525 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 from 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 solution:

A 3.3 % w/v solution of Lead (II) nitrate.

4. STORAGE CONDITION:

Store in a polyethylene container.