Question

A certain brand of iron supplement contains FeSO4·7H2O, which miscellaneous binders and fillers. Suppose 18.39 mL of the KMnO4 solution used in the question above are needed to oxidize Fe2+ to Fe3+ in a 0.5016 g pill. What is the percent of FeSO4·7H2O (molar mass 278.03 g mol-1) in the pill?

Answer 1

The percent of FeSO₄.7H₂O in the pill is 54.36%

Stoichiometry

The first part of the question is provided at the end of the answer.

The concentration of the KMnO₄ solution calculated from the first part of the question is 0.010666 M

Now, to determine the percent of FeSO₄.7H₂O in the pill

First, we will determine the mass of FeSO₄.7H₂O that reacted.

The balanced chemical equation for the oxidation reaction is

10FeSO₄.7H₂O + 2KMnO₄ + 8H₂SO₄ → 2MnSO₄ + 5Fe₂(SO₄)₃ + K₂SO₄ + 78H₂O

This means,

2 moles of KMnO₄ is required to oxidize 10 moles of FeSO₄.7H₂O

Now, we will determine the number of moles of KMnO₄ used in the reaction

Using the formula,

Number of moles = Concentration × Volume

Concentration = 0.010666 M

Volume = 18.39 mL = 0.01839 L

Then,

Number of moles KMnO₄ used = 0.010666 × 0.01839

Number of moles of KMnO₄ used = 1.9614774 × 10⁻⁴ mole

Now,

If 2 moles of KMnO₄ is required to oxidize 10 moles of FeSO₄.7H₂O

Then,

9.7467 × 10⁻⁴ mole of KMnO₄ will oxidize 5 × 1.9614774 × 10⁻⁴ mole of FeSO₄.7H₂O

5 × 1.9614774 × 10⁻⁴ = 9.807387 × 10⁻⁴

Thus, the number of moles of FeSO₄.7H₂O oxidized is 9.807387 × 10⁻⁴  mole

Now, for the mass of FeSO₄.7H₂O oxidized

Using the formula,

Mass = Number of moles × Molar mass

Then,

Mass of FeSO₄.7H₂O oxidized = 9.807387 × 10⁻⁴ × 278.03

Mass of FeSO₄.7H₂O oxidized = 0.2726748 g

Now, for the percent of FeSO₄.7H₂O in the pill

Percent of FeSO₄.7H₂O in the pill = $\frac{Mass\ of FeSO_{4}.7H_{2}O\ oxidized }{Mass\ of\ the\ pill} \times 100\%$

Then,

Percent of FeSO₄.7H₂O in the pill = $\frac{0.2726748}{0.5016} \times 100\%$

Percent of FeSO₄.7H₂O in the pill = 54.36%

Hence, the percent of FeSO₄.7H₂O in the pill is 54.36%

Here is the first part of the question:

If 29.11 mL of KMnO4 solution is required to oxidize 25.00 mL of 0.03105 M of Na2C2O4 solution, what is the concentration of KMnO4?

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