# A saturated solution of PbBr_2 is prepared by dissolving the solid salt in water. The concentration of Pb_2^+ in solution is found to be 0.0115 M. What is the Ksp for PbBr_2?

Jul 14, 2017

${K}_{s p} = 6.1 \times {10}^{-} 6$

#### Explanation:

We interrogate the solubility equilibrium.........

$P b B {r}_{2} \left(s\right) r i g h t \le f t h a r p \infty n s P {b}^{2 +} + 2 B {r}^{-}$

Now ${K}_{s p} = \left[P {b}^{2 +}\right] \left[B {r}^{-}\right]$.........And if we say that the solubility of $P b B {r}_{2} \equiv S$, then by stoichiometry........

${K}_{s p} = \left[S\right] {\left[2 S\right]}^{2} = 4 {S}^{3}$ (because $S = \left[P {b}^{2 +}\right]$, and $\left[B {r}^{-}\right] = 2 S$

$= 4 \times {\left(0.0115\right)}^{3} = 6.1 \times {10}^{-} 6$.........

Can you define what is meant by a $\text{saturated solution......?}$