Calcium oxalate, cac2o4 (m = 128.1), dissolves to the extent of 0.67 mg l-1. what is its ksp?

First balance the equation:

CaC2O4 (s) - > Ca2 + (aq) + C2O4 2 - (aq)

from the balanced equation, write Ksp:

Ksp=[Ca2+][C2O4] (Calcium oxalate is not included because it is a solid)

convert mg to g and then g/L into Molarity (Mol/L) to find the concentrations used in finding Ksp:

0.67mg/L x (1 g / 1000 mg) x (1 mol / 128.1 g) = 5.23e-6 M

Set up an ICE table from the balanced equation with previous calculation as the amount that has dissociated: (again, you can ignore Calcium oxalate because it is a solid and not included in Ksp)

CaC2O4 (s) - > Ca2 + (aq) + C2O4 (aq)

I - 0 0

C - + 5.23e-6 + 5.23e-6

E - + 5.23e-6 + 5.23e-6

You know have the concentrations of the species necessary for Ksp:

Ksp = (Ca2+) (C2O4)

= (5.23e-6) (5.23e-6)

Ksp = 2.74e-11