(2.a) [Pb+2] = 1.3 x 10 -3 M & [I-] = 2.6 x 10-3 M
Reminder that when the ions come only from the solid dissolving the concentrations are related.
| PbI2(s) | <---> | Pb+2(aq) | + | 2I-(aq) | |
| Initial (I) | 0 | 0 | |||
| Change(C) | +x | +x |
| Equilibrium (E) | x | x |
[I-] = 2[Pb+2] = 2x
Ksp = [Pb+2][I-]2
7.9 x 10-9 = (x)(2x)2 = (x)(4x2)
1.975 x 10-9 = x3
x = 1.3 x 10-9 M
2x = 2.6 x 10-9 M