Question

A 25 ml aliquot of of a solution containing Cu2+ and Ni2+ was treated with ascorbic acid at pH = 3 to reduce the Cu2+ ions. The pH was adjusted to 10.0 and 27.32 ml of of 0.0565 M M EDTA was required to reach a murexide end point. In a parallel titration, 40.45 ml of 0 .0565 M EDTA was required to reach a murexide end point in a 25 ml aliquot that was not treated with ascorbic acid.   What amounts of copper and Nickel in ppt (mass/volume) were in the original solution?

Answer 1

Initial volume = 50 ml

25 ml aliquot reacted with ascorbic acid

moles of EDTA used = 0.0565 M x 27.32 ml = 1.54358 mmol

moles of Ni2+ present = 1.54358 mmol

mass of Ni2+ present = 1.54358 mmol x 58.7 g/mol/1000 = 0.091 g

amount of Ni2+ in ppt = 2 x 0.091 g/50 ml = 3.64 x 10^-3 g/ml

Another 25 ml aliquot

EDTA used for Cu2+ + Ni2+ = 0.0565 M x 40.45 ml = 2.285425 mmol

moles of Cu2+ present = 2.285425 - 1.54358 = 0.741845 mmol

mass of Cu2+ present = 0.741845 mol x 63.546 g/mol = 0.04714 g

amount of Ni2+ in ppt = 2 x 0.04714 g/50 ml = 1.886 x 10^-3 g/ml