# Volumetric estimation of iron(II)ions

#### josephcollins

Hi ppl, I have an electrochemisry question. Explain why dilute sulphuric acid, rather than dilute hydrochloric acid, is used as a source of hydrogen ions in the volumetric estimation of iron (II) ions with potassium manganate (VII).

#### chem_tr

Gold Member
I don't think a difference would be present when you substitute sulfuric acid with hydrochloric acid. The redox reaction is as follows:

$$5 Fe^{2+} + MnO_4^- + 8 H^+ \rightarrow 5Fe^{3+} + Mn^{2+} + 4 H_2O$$

Here, you can substitute any anion for sulfate, providing that the acid is strong enough to react with permanganate to form water.

#### Borek

Mentor
josephcollins said:
Hi ppl, I have an electrochemisry question. Explain why dilute sulphuric acid, rather than dilute hydrochloric acid, is used as a source of hydrogen ions in the volumetric estimation of iron (II) ions with potassium manganate (VII).
Two things may happen in the presence od hydrochloric acid.

First, $$KMnO_4$$ is able to oxidize $$Cl^-$$ to $$Cl_2$$. Thus you will get a positive error in your determination result.

Second, $$Cl^-$$ anions will react with $$Fe^{3+}$$ anions to produce yellowish complex. This will make determination of end point more difficult and it will change redox potential of $$Fe^{2+}/Fe^{3+}$$ system. The latter shouldn't be a problem.

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#### chem_tr

Gold Member
I totally agree with this one. I think I will give away my "guru" title this year to someone deserving it better than me. Great work, Borek!

#### GCT

Homework Helper
Nah, keep it, you've contributed a fair amount to the forum; in addition, you're the only chemical researcher we have this forum. Share with us what you've learned so far, enlighten us guru;)

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