What is the solubility in moles/liter for iron(III) hydroxide at 25 oC given a Ksp value of 2.0 x 10-39. Write using scientific notation and use 1 or 2 decimal places (even though this is strictly incorrect!)

9.28 × 10⁻¹¹ mol/L

Explanation:

Let's consider the solution of iron(III) hydroxide.

Fe(OH)₃(s) ⇄ Fe³⁺(aq) + 3 OH⁻(aq)

We can relate the solubility (S) of the hydroxide with the solubility product (Ksp) using an ICE chart.

      Fe(OH)₃(s) ⇄ Fe³⁺(aq) + 3 OH⁻(aq)

I                              0                  0

C                            +S               +3S

E                              S                 3S

The solubility product is:

Ksp = [Fe³⁺] × [OH⁻]³ = S × (3S)³ = 27 S⁴

c is having 4 valence electrons and is bonded to three hydrogens and one sulphur atom, therefore, the number of bond pair is equal to four. as all the valence electrons are used in forming the bonds so, there is no lone pair left on carbon.

s is having 6 valence electrons and is bonded to one other sulfur atom and one carbon atom, therefore, the number of bond pair is equal to 2. as only two valence electrons are used in forming the bonds so, four electrons are left. therefore, two lone pairs are present on s.