Wustite has the non-stoichiometric composition $Fe X_{0.93} O$ , with iron present only as $Fe^{2 +}$ and $Fe^{3 +}$ . Find the percentage of iron atoms present as $Fe^{3 +}$ . Give the nearest integer.

Numerical answer type, answer in %, tolerance 0.5.

Answer: 15 %

Let the fraction of

Fe^{3 +}

f

. Charge balance:

0.93 (2 + f) = 2

, so

f = 2/0.93 - 2 = 0.1505

. That is

15.05%

, i.e. 15 to the nearest integer.