A 2.50\text{ g} sample of impure iron(III) oxide, \text{Fe}_2\text{O}_3, was completely re… — JAMB UTME

2.50\text{ g}

sample of impure iron(III) oxide,

\text{Fe}_2\text{O}_3

, was completely reduced by excess carbon(II) oxide gas to yield

1.40\text{ g}

of pure iron metal according to the equation:

\text{Fe}_2\text{O}_3(s) + 3\text{CO}(g) \rightarrow 2\text{Fe}(s) + 3\text{CO}_2(g)

What is the percentage purity of the iron(III) oxide sample? [

\text{Fe} = 56, \text{O} = 16, \text{C} = 12

]

The percentage purity of the iron(III) oxide sample is 80.0%.

According to the balanced chemical equation,

1\text{ mole}

\text{Fe}_2\text{O}_3

(

160\text{ g}

) yields

2\text{ moles}

\text{Fe}

(

112\text{ g}

). To obtain

1.40\text{ g}

of pure iron metal, the mass of pure

\text{Fe}_2\text{O}_3

required is

1.40 \times \frac{160}{112} = 2.00\text{ g}

. The percentage purity is calculated by taking the mass of pure

\text{Fe}_2\text{O}_3

divided by the total sample mass (

2.50\text{ g}

) multiplied by

100

, yielding

80.0\%

Calculate the molar mass of iron(III) oxide (

\text{Fe}_2\text{O}_3

) and total mass of iron produced per mole.

Molar mass of

\text{Fe}_2\text{O}_3 = 2(56) + 3(16) = 112 + 48 = 160\text{ g/mol}

. Mass of

2\text{ moles}

\text{Fe} = 2 \times 56 = 112\text{ g}

Stoichiometry shows

1\text{ mole}

\text{Fe}_2\text{O}_3

(

160\text{ g}

) produces

2\text{ moles}

\text{Fe}

(

112\text{ g}

Determine the mass of pure

\text{Fe}_2\text{O}_3

in the sample required to produce

1.40\text{ g}

\text{Fe}

\text{Mass of pure Fe}_2\text{O}_3 = 1.40\text{ g Fe} \times \frac{160\text{ g Fe}_2\text{O}_3}{112\text{ g Fe}} = 2.00\text{ g}

Mass proportions allow determination of the mass of reacting pure compound.

Calculate the percentage purity of the sample.

\text{Percentage purity} = \left(\frac{2.00\text{ g}}{2.50\text{ g}}\right) \times 100 = 80.0\%

Percentage purity is the ratio of pure component mass to total sample mass expressed as a percentage.

Determining percentage purity using stoichiometric mass calculations

Estimated Time:1m 30s

Question