Chapter 18, Problem 19E

Interpretation Introduction

Interpretation: The maximum molarity of calcium ions in hard water needs to be determined when the fluoride concentration is at the recommended level.

Concept Introduction: A constant that defines the solubility equilibrium that exists between a compound in its solid state and its ions in the aqueous state is said to be solubility product constant. Its general expression is written as:

  $\begin{array}{l}{\text{A}}_{\text{x}}{\text{B}}_{\text{y}}\text{(s)}\rightleftharpoons {\text{xA}}^{\text{+}}{\text{(aq) + yB}}^{\text{-}}\text{(aq)}\\ {\text{K}}_{\text{sp}}{\text{= [A}}^{\text{+}}{\text{]}}^{\text{x}}{{\text{[B}}^{\text{-}}}^{\text{]}}\end{array}$

Where K_sp is solubility product constant and square brackets represents concentration.

For slightly soluble compound ${\text{A}}_{\text{x}}{\text{B}}_{\text{y}}$ which contains ${\text{A}}^{n+}$ and $B^{m-}$ ions, the expression for equilibrium ionic product is given as:

  ${\text{Q = [A}}^{\text{n+}}{\text{]}}^{\text{x}}{{\text{[B}}^{\text{m-}}\text{]}}^{\text{y}}$