Question

Lead metal is added to 0.150 M Cr3+(aq).
Pb(s)+2Cr3+(aq)⇌Pb2+(aq)+2Cr2+(aq).
KC=3.2×10−10

What is [Pb2+] when equilibrium is established in the reaction?
What is [Cr2+] when equilibrium is established in the reaction?
What is [Cr3+] when equilibrium is established in the reaction?

Answer 1

...Pb(s)+2Cr3+(aq)⇌Pb2+(aq)+2Cr2+
I.......0.150.......0.........0
C.......-2x.........x.........2x
E.....0.150-2x......x.........2x

Kc = (Pb^2+)(Cr^3+)^2/(Cr^3+)^2

Substitute and solve for x = (Pb^2+). Note Pb(s) doesn't appear in the Kc expression since it is a pure substance.
The others you can get after you know x.