Chapter 17, Problem 5STP

Interpretation Introduction

Interpretation: $K_{sp}$ expression for the dissolution of $Pb{I}_{2(s)}$ in water is to be given.

Concept Introduction: $K_{sp}$ is known as the solubility product constant. It is the equilibrium constant for an equilibrium reaction of the dissolution of sparingly soluble salt in water. It is written as the product of the concentration of its constituent ions with each concentration term raised to the power equal to the coefficient as indicated in the balanced chemical equation.

Answer to Problem 5STP

Correct answer: $K_{sp}=\left[{\text{Pb}}^{\text{2+}}{}_{\text{(aq)}}\right]{\left[{\text{I}}^{\text{-}}{}_{\text{(aq)}}\right]}^{\text{2}}$

Explanation of Solution

Reason for correct option: The balanced equation for the equilibrium between ${\text{PbI}}_{\text{2 (s)}}$ and its constituting ions is given by the equation $Pb{I}_{2(s)}$ giving ${\mathrm{Pb}}^{2+}{}_{(aq)}+2I^{-}{}_{(aq)}$ The coefficient of ${\text{Pb}}^{2+}$ ions is 1 and that of ${\text{I}}^{-}$ is 2 and so are their powers in the expression.

Conclusion

Reasons for incorrect options: The coefficient of ${\text{Pb}}^{2+}$ ions and that of ${\text{I}}^{-}$ are not the same as their powers in the expression.