Question

A solution contains 1.26×10-2 M silver nitrate and 1.36×10-2 M calcium acetate. Solid ammonium sulfate is added slowly to this mixture. What is the concentration of calcium ion when silver ion begins to precipitate? [Ca2+] = ____M

Answer 1

Ksp of CaSO4 = 9.1*10^-6

Ksp of Ag2SO4 = 1.4*10^-5

CaSO4 ---> Ca+ 2 + So4-

Ksp = [Ca+2] [So4-2 ]

Ca[CH3COO]2 ---> Ca+2 + 2CH3COO-

[Ca+2] = 1.36*10^-2 M

(1.36*10^-2 ) * [SO4-2] =  9.1*10^-6

[SO4-2] = 6.69*10^-4 M

this much amount of sulphate needed for precipitation of CaSO4

For Ag2So4 precipitation

KSp = 1.4*10^-5 = [Ag+]^2 [ SO4-2]

[SO4-2] = 1.4*10^-5 / (1.26*10^-2)^2 = 0.088 M

this much amount needed for precipitation of Ag2SO4 The concentration of calcium ion when silver ion begins to precipitate is 9.1*10^-6 / 0.088 = [Ca+2] [Ca+2] = 1.034*10^-4 M