Question

The molar solubility of cobalt(II) sulfide in a 0.241 M sodium sulfide solution is ---- M. ksp value CoS=5.9x10^-21

Answer 1

Let molar solubility of Cobalt(II) sulfide be S mol/litre

We know that, the dissociation of Cobalt(II) sulfide can be given as,

CoS (s) + Aq ..........Co^2+ (aq) + S^2-(aq)

Also

Na2S (aq) ............ 2Na^+ (aq) + S^2- (aq)

0.482 0.241

But due to common ion effect concentration of S^2- is (S + 0.241)

Also given Ksp = 5.9 * 10^-21

Therefore,

Ksp = [Co^2+] [S^2-]

=(S)(S + 0.241)

Since, S<<<<<0.241 since solubility decreases in presence of common ion

Therefore,

S * 0.241 = 5.9. * 10^-21

S = 2.45 * 10^-20 mol/litre

S = 2.45 * 10^-20 M

Therefore the molar solubility of Cobalt (II) sulfide in a 0.241 M sodium sulfide solution is 2.45 * 10^-20 M.