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Topic: acidifying reagents  (Read 6134 times)

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yeung

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acidifying reagents
« on: September 23, 2005, 10:34:04 PM »
Why do we use dilute sulphuric acid to acidify potassium permangate solution, but not hydrochloric acid or nitric acid?

Offline xiankai

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Re:acidifying reagents
« Reply #1 on: September 24, 2005, 03:41:02 AM »
the latter are sufficiently stronger reducing agents than the former.

using them would defeat the purpose of KMnO4 solution.
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Offline Borek

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Re:acidifying reagents
« Reply #2 on: September 24, 2005, 10:01:38 AM »
the latter are sufficiently stronger reducing agents than the former.

Cl- can be oxidised to Cl2 - that's OK.

But what do you want NO3- to be oxidised to?

I would rather expect NO3- to add to MnO4- oxidation, making stoichiometry of the reaction dubious.
« Last Edit: September 24, 2005, 10:02:41 AM by Borek »
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yeung

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Re:acidifying reagents
« Reply #3 on: September 25, 2005, 12:52:12 AM »
Why do we need to acidify the solution?

Offline Donaldson Tan

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Re:acidifying reagents
« Reply #4 on: September 25, 2005, 02:03:27 AM »
MnO4- + 8H+ + 5e <-> Mn2+ + 4H2O

the oxidising power of potassium permanganate is governed by the above equation. The forward reaction is favoured (Le Chateliter's Principle) in an acidic medium.

The only reason why dilute sulphuric acid is the preferred acid medium is because not only it provides H+, but also HSO4- and SO42- are not easily oxidised/reduced to yield unwanted products.
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