Chapter 15, Problem 81QRT

(a)

Interpretation Introduction

Interpretation:

Out of ${\text{Ca}}_3{\left({\text{PO}}_4\right)}_2$ or ${\text{AlPO}}_4$, the one that is precipitated first has to be predicted.

Concept Introduction:

The solubility product for an equilibrium reaction is defined as the product of ion concentration raised to power their stoichiometric coefficient.  The symbol for solubility product is $K_{\text{sp}}$.  If $K_{\text{sp}}$ value is higher, it means that compound is highly soluble.

The precipitation takes place due to the different solubilities of the two ionic compounds.  The compound which is more soluble will remains in the solution whereas less soluble compound precipitates first.

(b)

Interpretation Introduction

Interpretation:

The concentration of first cation species when second cation species starts to precipitate has to be calculated.

Concept Introduction:

The solubility product for an equilibrium reaction is defined as the product of ion concentration raised to power their stoichiometric coefficient.  The symbol for solubility product is $K_{\text{sp}}$.