chemistry stuck pleas help?

Question

At saturation, 5.5 x 10-4 moles of PbI2 have dissolved in 1 liter of water. What is Ksp for PbI2 at this temperature?

someone tried to explain it but it doesnt make any sense? so help please

Ksp=Solubility product constant (Ksp)

Answer 1

Ksp = [Pb++][I-]^2

PbI2 <===> Pb++ + 2I-
5.5x10^-4M PbI2 ===> 5.5x10^-4MPb++ + 11x10^-4MI- (=1.1x10^-3MI-)

Ksp = (5.5x10^-4)(1.1x10^-3)^2
= (5.5x10^-4)(1.21x10^-6)
= 6.05x10^-10

The PbI2 that dissolves is 5.5x10*minus4*M So the [Pb++] is 5.5x10*minus4* and the [I-] is 11x10*minus4*. In the Ksp expression, [I-] is squared. So I re-express that as 1.1x10*minus3 before squaring it, to keep all the numbers in a reasonable range.