Substance Ksp A solution of Na2CO3 is added dropwise to a so

Substance Ksp

A solution of Na2CO3 is added dropwise to a solution that contains 1.14×10−2 M Fe^2+  and 1.53×10−2 M Cd^2

+ . What concentration of CO3^2- is need to initiate precipitation? Neglect any volume changes during the addition.

PART B

In the solution from Part A, what will the concentration of CO3^2 be when begins to precipitate?

Solution

Part A -

For FeCO3, Ksp = [Fe2+][CO3 2-] 2.10 x 10^-11 = (1.14 x 10^-2)[CO3 2-] [CO3 2-] = 1.84 x 10^-9 M

For CdCO3, Ksp = [Cd2+][CO3 2-] 1.80 x 10^-14 = (1.53 x 10^-2)[CO3 2-] [CO3 2-] = 1.18 x 10^-12 M

PART B -

In the solution from Part A, the concentration of CO3^2 will be 1.18 x 10^-12 M when precipitation begins as CdCO3 precipitates early.