Ksp to Molar Solubility

Slightly soluble salts (see data table page 802)

Molar solubility of the slightly soluble salt identifies the degree
 to which the salt actually dissolves in water.
Expressed in mol/L
The concentration of the ions at llbm is related to the molar solubility of
the salt  by the mole relationship in the balanced llbm equation.

example Determine the molar solubility of iron (II) hydroxide.

1.Write the llbm dissociation reaction.
2. Write the Ksp expression.
3.Complete the ICE chart. (not considering solids - llbm reaction, solid concentration will not change)
4.Determine the value of "x"
5.State the molar solubility value.

            Fe(OH)2(s)        <=>         Fe2+ (aq)        +      2OH-(aq)

I            n/a                                    0                           0
C          n/a                                    +x                         +2x
E          n/a                                     x                           2x

     Ksp = [Fe3+][OH-]2
4.9x10-17 = (x)(2x)2
4.9x10-17 = 4x3
2.3x10-6 = x

The molar solubility of Fe(OH)2 is 2.3x10 -6 mol/L.
[According to the balanced llbm equation, for every mole of Fe2+ that shows up at llbm, one mole of Fe(OH)2 had to dissolve.]

Homework:
p486: 1,2,3
p493: 4,5,6