Chapter 5, Problem 94RQ

A 1.362 g sample of an iron ore that contained ${\text{Fe}}_{\text{3}}{\text{O}}_{\text{4}}$ was dissolved in acid and all of the iron was reduced to ${\text{Fe}}^{\text{2+}}$. The solution was then acidified with ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ and titrated with 39.42 mL of 0.0281 M ${\text{KMnO}}_{\text{4}}$, which oxidized the iron to ${\text{Fe}}^{\text{3+}}$. The net ionic equation for the reaction is

${\text{5Fe}}^{\text{2+}}{\text{+ MnO}}_{\text{4}}{}^{\text{-}}{\text{+ 8H}}^{\text{+}}\to {\text{ 5Fe}}^{\text{3+}}{\text{+ Mn}}^{\text{2+}}{\text{+ 4H}}_{\text{2}}\text{O}$

(a) What was the percentage by mass of iron in the ore?

(b) What was the percentage by mass of ${\text{Fe}}_{\text{3}}{\text{O}}_{\text{4}}$ in the ore?