Question

A solution contains 1.694 g of cobalt sulphateCoSO4per litre. Calculate: (1.5)a) the volume of 0.008640 M EDTA solution required to titrate 25.0 mLof the cobalt solution. b) the volume of a 0.009450 M Zn solution required for titrating the excess of EDTA if 50.00 mL of the 0.008640 M EDTA solution had previously been added to 25.00 mL of the initial solution. c) the volume of 0.008640 M EDTA solution required to titrate Zn2+being displaced by Co2+after the addition of an excess of ZnY2-to 25.00 mL of the CoSO4 solution.

Answer 1

a) Co²⁺ + YH₂^2- CoY^2- + 2H⁺

31.54 mL of EDTA solution 0.008640M

b) mmol of Co²⁺ of the initial solution: 0.2725mmol

excess of EDTA = 0.432 mmol - 0.2725 mmol = 0.1595 mmol

Zn²⁺ + YH₂^2- ZnY^2- + 2H⁺

16.88 mL of Zn²⁺ solution 0.009450M

c) Note: You need to know the excess volume of ZnY^2- added, but we can assume that is molar equivalent to the amount of Co²⁺ in 25mL of initial solution.

Co²⁺ + ZnY^2- CoY^2- + Zn²⁺

Zn²⁺ + YH₂^2- ZnY^2- + 2H⁺

mmol of Co²⁺ of the initial solution: 0.2725mmol

mmol of 0.08640 M EDTA solution: 0.2725mmol

Volume of EDTA solution: 31.54 mL