Scandium fluoride, ScF3, is practically insoluble in water. a) Calculate the sol

ID: 634737 • Letter: S

Question

Scandium fluoride, ScF3, is practically insoluble in water.

a) Calculate the solubility of ScF3 in pure water. (You may neglect the hydrolysis of the fluoride

ion as it has a negligible impact on the overall solubility.)

b) Calculate the concentrations of all aqueous species in a saturated solution of ScF3.

c) Scandium fluoride is somewhat more soluble in acidic solution. Determine the molar solubility

of ScF3 in 1.00 M HNO3.

d) Scandium fluoride is somewhat less soluble in the presence of NaF. Determine the molar

solubility of ScF3 in 0.050 M NaF.

Ksp (ScF3) = 4.2

a) Let, the solubility of ScF3 is x M.

ScF3 -> Sc3+ + 3F-

Ksp = [Sc3+][F-]^(3)

=> Ksp = x*(3x)^3 =27x^(4)

x = 2*10^(-5) M

b)[Sc3+]=2*10^(-5) M

[F-]=3[Sc3+] = 6*10^(-5)

[ScF3] is fairly the same, because it is given that it is practically inslouble in water.

c)[H+]=1.0M

ScF3 -> Sc+++ + F3-

H+ + F- -> HF

Ka = 6.3 * 10^(-4)

Ka = [H+][F-]

[H+]=1 M

[F-]=6.3*10^(-4) M

[Sc+++]= Ksp/27[F-]^(3) = 6.22 * 10^(-10) M

d)[F-] = 0.05M

Ksp = x*(3*0.05)^3

=> x=Ksp/0.15^3 =1.24*10^(-15) M

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