# An aqueous solution of lead II phosphate is added to an aqueous solution of potassium iodide. When the two colorless solutions mix, a bright yellow precipitate forms in a double replacement reaction. What is the balanced chemical equation?

$P b H P {O}_{4} \left(a q\right) + 2 K I \left(a q\right) \rightarrow P b {I}_{2} \left(s\right) \downarrow + K {H}_{2} P {O}_{4}$
This question is unfortunate as phosphate salts tend to be as soluble as bricks, and lead phosphate, $P {b}_{3} {\left(P {O}_{4}\right)}_{2}$ would be even more insoluble. Thus I have assumed a biphosphate salt; $H P {O}_{4}^{2 -}$ can have some solubility (at any rate phosphate ion, $P {O}_{4}^{3 -}$, is fairly rare, and speciates to $H P {O}_{4}^{2 -}$ in aqueous solution).