[gear2d]

Will PbBr2 precipitate if student mixes .0001M of Pb²⁺ with 0.00005M Br^- (Ksp of PbBr2 = 4.6x10^-6)?

My problem with is when calculating the ion product. The math:

Ksp = [Pb²⁺][2Br]²

4.6x10^-6 = .0001M * 0.00005M²

From this I see that the ion product (right hand side of math above) is less then the Ksp and there for no precipitant.

But, why is it that you have to do 0.00005M² and not [2*0.00005M]²?

A general question, what will happen to Ksp with increasing temp (general case)?

[Astrokel]

hey gear2d,

remember the stoichiometric coefficient of an ion is the power of its concentration in the K_sp expression. Therefore you do not include it in the calculation of concentration. Ksp generally increases with temperature for most salts.

[AWK]

Ksp = [Pb2+][2Br]2

?

K_sp = [Pb²⁺][ Br]² is a correct formula

When you calculate solubilization of PbBr₂ in water then you should use a stoichiometric concentration of bromide  (factor 2).
When you have an external source of bromide you should use its  real concnetration.