Question

The solubility of Al(OH)3 is measured and found to be 2.22×10-7 g/L. Use this information to calculate a Ksp value for aluminum hydroxide. Ksp =

Answer 1

Molar mass of Al(OH)3,
MM = 1*MM(Al) + 3*MM(O) + 3*MM(H)
= 1*26.98 + 3*16.0 + 3*1.008
= 78.004 g/mol


Molar mass of Al(OH)3= 78.004 g/mol
s = 2.22*10^-7 g/L
To covert it to mol/L, divide it by molar mass
s = 2.22*10^-7 g/L / 78.004 g/mol
s = 2.846*10^-9 g/mol

At equilibrium:
Al(OH)3   <---->     Al3+     +         3 OH-   

                     s                  3s      

Ksp = [Al3+][OH-]^3
Ksp = (s)*(3s)^3
Ksp = 27(s)^4
Ksp = 27(2.846*10^-9)^4
Ksp = 1.771*10^-33
Answer: 1.771*10^-33