a) Calculate pH of saturated solution of dicalcium phosphate (CaHPO4) in water if its solubility is 3.16x10-4 m.

CaHPO4(aq)-> Ca^2+(aq) + HPO4^2-(aq)

Although phosphoric acid is a triprotic acid, consider only pKa'' since pKa' and pKa''' will not contribute to this dissociation:

H2PO4^-(aq)->H+(aq)+ HPO4^2-(aq), pKa''=6.8

Assume that:

• CaHPO4 is a strong electrolyte;

• Ionic strength of CaHPO4 in water is negligible due to low concentration

b) How much solubility of CaHPO4 will change when 1.0x10-3 m MgCl2 is added to the same saturated solution of dicalcium phosphate?

Assume that :

• MgCl2 is a strong electrolyte and very soluble in water;

• Ionic strength cannot be ignored;

• Precision of a single iteration, whenever necessary, is sufficient;