Given the solubility of Ca3(PO4)2 is Wg/100mL. The solubility in mol/L is S=MW×1001000mol/L.
The equilibrium reaction of calcium phosphate is
AtequilibriumCa3(PO4)2⇌3Ca2+3S+2PO43−2S
Now, Ksp=[Ca2+]3[PO43−]2
⇒Ksp=(3S)3(2S)2=108×S5
⇒Ksp=108×(MW×10)5⇒Ksp=108×105×(MW)5
=1.08×107(MW)5