Question

What is the molar solubility product for V3(PO4)5 in terms of KSP?

(a) S = (KSP/84375)^1/8

(b) S = KSP^1/8

(c) S = (KSP/15)^1/8

(d) S = (KSP/108)^1/8

I had been asked this question during an online interview.

I need to ask this question from Solubility Solutions in chapter Solutions of Chemistry – Class 12

Answer 1

Right option is (a) S = (KSP/84375)^1/8

To explain: The dissociation reaction is represented as V3(PO4)5 → 3V^5+ + 5PO4^3-

If S is the solubility of V^5+ and PO4^3- ions then KSP = [3V^5+]^3 [5PO4^3-]^5, where the square brackets indicate the molar concentrations of the ions in the solution. KSP can then be written as KSP = [3S] ^3[5S] ^5 = 3^3 x 5^5 x S^8 gives KSP=  84375 x S^8.

Therefore, on rearranging, S = (KSP/84375)^1/8.