1. From the solubility data given for the following compounds, calculate their solubility product
constants. a. Cu SCN , copper(I) thiocyanate, 4.9 × 10-4 g L Ksp = b. Ag Br, silver bromide,
1.1 x 10-6 g/10 mL c. Ca3 (PO4)2, calcium phosphate, 1.2 × 10-3 g/L d. Ag,CrO4, silver
chromate, 0.043 mg/mL K,
Solution
a)
s = 4.9*10^-4 g/L
Molar mass of CuSCN,
MM = 1*MM(Cu) + 1*MM(S) + 1*MM(C) + 1*MM(N)
= 1*63.55 + 1*32.07 + 1*12.01 + 1*14.01
= 121.64 g/mol
Molar mass of CuSCN= 121.64 g/mol
s = 4.9*10^-4 g/L
To covert it to mol/L, divide it by molar mass
s = 4.9*10^-4 g/L / 121.64 g/mol
s = 4.028*10^-6 g/mol
At equilibrium:
CuSCN <----> Cu+ + SCN-
s s
Ksp = [Cu+][SCN-]

2. Ksp = (s)*(s)
Ksp = 1(s)^2
Ksp = 1(4.028*10^-6)^2
Ksp = 1.623*10^-11
Answer: 1.6*10^-11
b)
s = 1.1*10^-6 g/10 mL
= 1.1*10^-7 g/mL
= 1.1*10^-4 g/L
Molar mass of AgBr,
MM = 1*MM(Ag) + 1*MM(Br)
= 1*107.9 + 1*79.9
= 187.8 g/mol
Molar mass of AgBr= 187.8 g/mol
s = 1.1*10^-4 g/L
To covert it to mol/L, divide it by molar mass
s = 1.1*10^-4 g/L / 187.8 g/mol
s = 5.857*10^-7 g/mol
At equilibrium:
AgBr <----> Ag+ + Br-
s s
Ksp = [Ag+][Br-]
Ksp = (s)*(s)

3. Ksp = 1(s)^2
Ksp = 1(5.857*10^-7)^2
Ksp = 3.43*10^-13
Answer: 3.4*10^-13
c)
s = 1.2*10^-3 g/L
Molar mass of Ca3(PO4)2,
MM = 3*MM(Ca) + 2*MM(P) + 8*MM(O)
= 3*40.08 + 2*30.97 + 8*16.0
= 310.18 g/mol
Molar mass of Ca3(PO4)2= 310.18 g/mol
s = 1.2*10^-3 g/L
To covert it to mol/L, divide it by molar mass
s = 1.2*10^-3 g/L / 310.18 g/mol
s = 3.869*10^-6 g/mol
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(3.869*10^-6)^5
Ksp = 9.36*10^-26

4. Answer: 9.36*10^-26
d)
s = 0.043 mg/mL
s = 0.043 g/L
Molar mass of Ag2CrO4,
MM = 2*MM(Ag) + 1*MM(Cr) + 4*MM(O)
= 2*107.9 + 1*52.0 + 4*16.0
= 331.8 g/mol
Molar mass of Ag2CrO4= 331.8 g/mol
s = 4.3*10^-2 g/L
To covert it to mol/L, divide it by molar mass
s = 4.3*10^-2 g/L / 331.8 g/mol
s = 1.296*10^-4 g/mol
At equilibrium:
Ag2CrO4 <----> 2 Ag+ + CrO42-
2s s
Ksp = [Ag+]^2[CrO42-]
Ksp = (2s)^2*(s)
Ksp = 4(s)^3
Ksp = 4(1.296*10^-4)^3
Ksp = 8.706*10^-12
Answer: 8.7*10^-12