Q.

Solubility of calcium phosphate (molecular mass, M) in water is Wg per 100 mL at 25 °C. Its solubility product at 25 °C will be approximately.           [2024]

1 107(WM)3  
2 103(WM)5  
3 107(WM)5  
4 105(WM)5  

Ans.

(3)          

               Mass of calcium phosphate dissolved in 100 mL water = W g

               Mass of calcium phosphate dissolved in 1L (1000mL) water (WCa3(PO4)2)=10wg

               Molar mass of calcium phosphate (MCa3(PO4)2)=M gmol-1

               Molar solubility (s) is the moles of calcium phosphate dissolved in 1 L water = WCa3(PO4)2MCa3(PO4)2=10wM

                Ca3(PO4)23Ca2+3s+2PO43-2s

                Solubility product,

                Ksp=[Ca2+]3[PO43-]2=[3s]3[2s]2=108s5=108×(10wM)5107×(wM)5