Question

The solubility product of As2O3 is 10.8 x 10-9
It is 50% dissociated in saturated solution.
The solubility of salt is
(a) 10-2
(b) 2x 10-20
(c) 5 x 10-3 (d) 5.4 x 10-9​

Answer 1

solubility of salt is 2 × 10^-2

given, solubility product of As2O3 , Ksp = 10.8 × 10^-9.

let solubility of salt is S. dissociation reaction of salt will be ....

As2O3 ⇔ 2As^3+ + 3O^-

at t = 0, S 0 0

at t = t0, S - S/2 S/2 S/2 [ as 50% dissociation in saturated solution. ]

now Ksp = [2As³+ ]² [3O^-]³

= (2s/2)²(3s/2)³

= s² × 27s³/8

= 27s^5/8

⇒10.8 × 10^-9 = 27 s^5/8

⇒4 × 8 × 10^-10 = s^5

⇒s = 2 × 10^-2

hence solubility of salt is 2 × 10^-2 . option (b) is correct choice.