A sample of ferrous oxide has the composition Fe_0.93O. Assuming only Fe^2+ and Fe^3+ are present, calculate the percentage of the iron present as Fe^3+ (nearest integer).

JEE Main levelNumerical answerDifficulty 2 of 3ss191

A sample of ferrous oxide has the composition $Fe X_{0.93} O$ . Assuming only $Fe X^{2 +}$ and $Fe X^{3 +}$ are present, calculate the percentage of the iron present as $Fe X^{3 +}$ (nearest integer).

Numerical answer type, answer in %, tolerance 0.5.

For 0.93 Fe per O, total positive charge must be 2. Let

Fe X^{3 +} = y

, so

2 (0.93 - y) + 3 y = 2

, giving

y = 0.14

and

Fe X^{2 +} = 0.79

. Percentage of

Fe X^{3 +} = 0.14/0.93 \times 100 = 15.05%

, about 15%.