Question

A solution contains 1.53 mg of CoSO₄ (155.0 grams/mole) per mL. Calculate the volume (in mL) of 0.009423 M Zn²⁺ needed to titrate the excess complexing reagent after the addition of 80.00 mL of 0.008942 M EDTA to a 20.00 mL aliquot of the Co²⁺ solution.

Answer 1

After addition of 80 ml of EDTA the solution becomes = 20 + 80 = 100 ml

as the no of moles of CoSO4 = given mass / molar mass = 1.53 / 155 = 0.00987

molarity =no of moles / volume of solution = 0.00987 /20 = 0.0049 moles

excess of EDTA = concentration of EDTA - concentration of CoSO4 = 0.00894 - 0.0049 = 0.00404 M

As M1V1 ( Excess of EDTA ) = M2V2 ( ZN2+)

0.00404M * 100 ml =  0.009423 M * V2

and V2 = 42.887 ml needed to titrate the excess complexing reagent .