Question

+-/0.1 points 40. 0/4 Submissions Used (a) If the molar solubility of Ca3(PO4)2 at 25 °C is 4.53e-08 mol/L, what is the Ksp at this temperature? Ksp (b) It is found that 8.70e-09 g of Ga(OH)3 dissolves per 100 mL of aqueous solution at 25 °C. Calculate the solubility-product constant for Ga(OH)3 Ksp (c) The Ksp of Cd3(PO4)2 at 25 °C is 2.53e-33. What is the molar solubility of Cd3(PO4)2? solubility mol/L

Answer 1

a)

At equilibrium:

Ca3(PO4)2 <----> 3 Ca2+ + 2 PO43-

   3s 2s

Ksp = [Ca2+]^3[PO43-]^2

Ksp = (3s)^3*(2s)^2

Ksp = 108(s)^5

Ksp = 108(4.53*10^-8)^5

Ksp = 2.06*10^-35

Answer: 2.06*10^-35

b)

s = 8.70*10^-9 g / 100 mL

= 8.70*10^-9 g / 0.100 L

= 8.70*10^-8 g / L

Molar mass of Ga(OH)3,

MM = 1*MM(Ga) + 3*MM(O) + 3*MM(H)

= 1*69.72 + 3*16.0 + 3*1.008

= 120.744 g/mol

Molar mass of Ga(OH)3= 120.744 g/mol

s = 8.7*10^-8 g/L

To covert it to mol/L, divide it by molar mass

s = 8.7*10^-8 g/L / 120.744 g/mol

s = 7.205*10^-10 mol/L

At equilibrium:

Ga(OH)3 <----> Ga3+ + 3 OH-

   s 3s

Ksp = [Ga3+][OH-]^3

Ksp = (s)*(3s)^3

Ksp = 27(s)^4

Ksp = 27(7.205*10^-10)^4

Ksp = 7.277*10^-36

Answer: 7.28*10^-36

c)

At equilibrium:

Cd3(PO4)2 <----> Cd2+ + 2 PO43-

   s 2s

Ksp = [Cd2+][PO43-]^2

2.53*10^-33=(s)*(2s)^2

2.53*10^-33= 4(s)^3

s = 8.584*10^-12 M

Answer: 8.58*10^-12 M