Question

Arrange the salts by their molar solubility in water. Consult the table of solubility product constants for the Ksp value for each salt. Most soluble Least soluble Answer Bank Mg; (PO4)2 Baso, Al(OH), CaF,

Answer 1

Ksp of Mg3(PO4)2   = 1*10^-25

Mg3(PO4)2(s) ---------------> 3Mg^2+ (aq) + 2PO4^3- (aq)

-------------------------------------- 3s -----------   2s

Ksp   = [Mg^2+]^3[PO4^3-]^2

1*10^-25   = (3s)^3(2s)^2

1*10^-15   = 108s^5

s = 4*10^-4 M

molar solubility of Mg3(PO4)2

Ksp of BaSo4   = 1.5*10^-9

BaSO4(s) -----------> Ba^2+ (aq) + SO4^2- (aq)

------------------------- s ----------- s

Ksp    = [Ba^2+][SO4^2-]

Ksp   = s*s

1.5*10^-9 = s^2

s = 3.87*10^-5

molar solubility of BaSO4 = 3.87*10^-5M

Ksp of Al(OH)3 = 1*10^-33

Al(OH)3(s) -----------. Al^3+ (aq) + 3OH^- (aq)

-----------------------   s   ------------ 3s

Ksp    = [Al^3+][OH^-]^3

1*10^-33 = s*(3s)^3

s = 2.5*10^-9

molar solubility of Al(OH)3 = 2.5*10^-9 M

Ksp of CaF2   = 3.9*10^-11

CaF2(s) -------------> Ca^2+ (aq) + 2F^- (aq)

------------------------ s -------------- 2s

Ksp    = [Ca^2+][F^-]^2

3.9*10^-11         = s*(2s)^2

s = 2*10^-4

The molar solubility of CaF2 = 2*10^-4 M

most soluble

CaF2

Mg3(PO4)2

BaSO4

Al(OH)3

least soluble