# Understanding how to choose the right reaction for electrochemistry [closed]

I am quite new here and studying a bit of electrochemistry. In the course of my studies I encountered a problem I couldn't figure out:

A sample of iron ore weighing $\pu{0.2792 g}$ was dissolved in an excess of a dilute acid solution. All the iron was first converted to $\ce{Fe(II)}$ ions. The solution then required $\pu{23.30 mL}$ of $\pu{0.0194 M}$ $\ce{KMnO4}$ for oxidation to $\ce{Fe(III)}$ ions. Calculate the percent by mass of iron in the ore.

Having thought about this question somewhat, it is clear that I will have to use the redox reactions for iron of

\begin{align} \ce{Fe^0(s) &-> Fe^2+ + 2e-} \\ \ce{Fe^2+ &-> Fe^3+ + e-} \end{align}

Furthermore, seeing as the reaction is occurring in an acidic environment, I thought to make the assumption that $\ce{KMnO4}$ will dissociate into its constituent ions, leaving me with picking between either the reaction of

$$\ce{MnO4^- + 2H2O + 3e- -> MnO2 + 4OH-}$$

or

$$\ce{MnO4^- + 8H+ + 5e- -> Mn^2+ + 4H2O}$$

When it comes to the technical working of this problem I think I can sort it out, but my issue resides in finding the correct mechanism. If anyone is willing to help me out with what I am sure is a simple problem for the experienced members of this community, I would be extremely grateful.

In addition to this I was wondering if anyone could recommend a resource to learn more holistically about these sorts of reactions, as this question in my textbook is part of the challenge portion, and hence there is not as much material regarding the exact mechanisms of these processes.

## closed as too broad by Mithoron, Todd Minehardt, airhuff, DSVA, WildcatAug 1 '17 at 11:50

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• I wish there was a tag called classic (for titration and redox reactions) – bonCodigo Jul 31 '17 at 23:26