To calculate the concentration of Cd2+ when Fe2+ starts to precipitate:
CO32- from soluble Na2CO3 will react with ions in solution to form precipitates:
Fe2+(aq) + CO32-(aq) ⇌ FeCO3(s) → Ksp = 2.10 x 10-11
Cd2+(aq) + CO32-(aq) ⇌ CdCO3(s) → Ksp = 1.80 x 10-14
We will construct an ICE Chart to determine the concentration of CO32- needed to start precipitation of FeCO3:
The Ksp expression for FeCO3 is:
**Solids are ignored in the Ksp expression
Solve for x,
x = [CO32-] = 1.479 x 10-9 M CO32-
A solution of Na2CO3 is added dropwise to a solution that contains 1.14 x 10-2 M Fe2+ and 1.50 x 10-2 M Cd2+.
What will be the concentration of Cd2+ be when Fe2+ begins to precipitate? Express the molar concentrations numerically.
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