# Problem 6. The dissolution/precipitation of struvite occurs according to \mathrm{MgNH}_{4} \mathrm{PO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}_{(\mathrm{s})}=\mathrm{Mg}^{2+}+\mathrm{NH}_{4}^{+}+\mathrm{PO}_{4}^{3-}+6 \mathrm{H}_{2} \mathrm{O} The equilibrium expression for the dissolution is a"solubility product and has the form K_{\mathrm{sp}}=\left[\mathrm{Mg}^{2-}\right]\left[\mathrm{NH}_{4}^{+}\right]\left[\mathrm{PO}_{4}^{3-}\right]

Calculate the value of [Mg] needed to make the solution just saturated with struvite. (If you were trying to precipitate struvite, for these pH, Amr, and PT conditions, you would have to raise [Mg] above this level.)