Edetate disodium titrant
Dissolve 18.6 g of edetate disodium in water to make 1000 mL, and standardize the solution as follows. Weigh accurately about 2 g of aluminum wire, transfer to a 1000-mL volumetric flask, and add 50 mL of a mixture of hydrochloric acid and water (1:1). Swirl the flask to ensure contact of the aluminum and the acid, and allow the reaction to proceed until all of the aluminum has dissolved. Dilute with water to volume, and mix. Pipet 10 mL of this solution into a 250-mL beaker, add, in the order named and with continuous stirring, 25.0 mL of
Edetate disodium titrant and 20 mL of acetic acidammonium acetate buffer TS, and boil gently for 5 minutes. Cool, and add 50 mL of alcohol, and 2 mL of
dithizone TS. Titrate with 0.05
M zinc sulfate VS to a bright rose-pink color. Perform a blank determination, substituting 10 mL of water for the aluminum solution, and make any necessary correction. Calculate the molarity of the solution taken by the formula:
W / 26.98V,
in which
W is the weight, in mg, of aluminum in the portion of solution taken; and
V is the volume, in mL, of
Edetate disodium titrant consumed.
Procedure
Transfer about 800 mg of Ammonium Alum, accurately weighed, to a 400-mL beaker, moisten with 1 mL of glacial acetic acid, and add 50 mL of water, 50.0 mL of
Edetate disodium titrant, and 20 mL of acetic acid-ammonium acetate buffer TS. Warm on a steam bath until solution is complete, and boil gently for 5 minutes. Cool, add 50 mL of alcohol and 2 mL of
dithizone TS, and titrate with 0.05 M zinc sulfate VS to a bright rose-pink color. Perform a blank determination, and make any necessary correction. Each mL of 0.05 M
Edetate disodium titrant is equivalent to 11.86 mg of AlNH
4(SO
4)
2.