Question

The amount of iron in a meteorite can be determined by a redox titration using KMnO4 as the titrant. A 0.4158 g sample of meteorite is dissolved in acid and the dissolved Fe3+ is reduced to Fe2+. Titration of the Fe2+ with 0.0262 M KMnO4 requires 39.84 mL to reach the end point. a) Use appropriate half-reactions to write the balanced reaction equation for the titration of MnO4– with Fe2+

b) Determine the %Fe in the sample of meteorite.

Answer 1

(a) In balanced chemical reaction, both charge and atoms are equal on both side of reaction

Reaction between MnO₄^- and Fe²⁺ is:

8H⁺ + 5Fe²⁺ + MnO₄^- 5 Fe³⁺ + Mn²⁺ + 4H₂O

(b) Molarity of KMnO₄ = 0.0262 M

Volume of KMnO₄ = 39.84 mL = 0.03984 L

Moles of KMnO₄ = Molarity * Volume = 0.0262 M*0.03984 L = 0.001044 mol

From reaction

1 mol of KMnO₄ reacts with 5 mol of Fe²⁺

Thus, Moles of Fe²⁺ titrated = 5* moles of KMnO₄ = 5* 0.001044 mol = 0.005219 mol

Molar mass of Fe = 55.8 g/mol

Mass of Fe in sample = Moles of Fe²⁺ * molar mass of Fe = 0.005219 mol * 55.8 g/mol = 0.2912 g

% Fe in sample = (Mass of Fe / Total mass of sample) *100%

= (0.2912 g / 0.4158g)*100% = 70.04 %