Volumetric estimation of iron(II)ions

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

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

[tex]5 Fe^{2+} + MnO_4^- + 8 H^+ \rightarrow 5Fe^{3+} + Mn^{2+} + 4 H_2O[/tex]

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

Borek

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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, [tex]KMnO_4[/tex] is able to oxidize [tex]Cl^-[/tex] to [tex]Cl_2[/tex]. Thus you will get a positive error in your determination result.

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


Chemical calculators for labs and education
BATE - pH calculations, titration curves, hydrolisis
 
Last edited:

chem_tr

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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! :approve:
 

GCT

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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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