Question

Which of the following has the greatest solubility in water?
(A) ZnCr2O4 ( Ksp = 2.7 x 10-8)	(B) BaCrO4 ( Ksp = 2.3 x 10-10 )
(C) CaF2 ( Ksp = 3.9 x 10-11)	(D) AgBr ( Ksp = 5.0 x 10-13 )

Answer 1

The salt dissolves as:

ZnCrO4 <----> Zn2+ + CrO42-

   s s

Ksp = [Zn2+][CrO42-]

2.7*10^-8=(s)*(s)

2.7*10^-8= 1(s)^2

s = 1.643*10^-4 M

The salt dissolves as:

BaCrO4 <----> Ba2+ + CrO42-

   s s

Ksp = [Ba2+][CrO42-]

2.3*10^-10=(s)*(s)

2.3*10^-10= 1(s)^2

s = 1.517*10^-5 M

The salt dissolves as:

CaF2 <----> Ca2+ + 2 F-

   s 2s

Ksp = [Ca2+][F-]^2

3.9*10^-11=(s)*(2s)^2

3.9*10^-11= 4(s)^3

s = 2.136*10^-4 M

The salt dissolves as:

AgBr <----> Ag+ + Br-

   s s

Ksp = [Ag+][Br-]

5*10^-13=(s)*(s)

5*10^-13= 1(s)^2

s = 7.071*10^-7 M

The compound with maximum solubility is:

CaF2

Answer: CaF2