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Topic: Why does phosphoric acid H3P04 not act as an oxidant?  (Read 370 times)

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Offline lloyd709

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Why does phosphoric acid H3P04 not act as an oxidant?
« on: January 25, 2024, 04:23:49 AM »
On googling this all I can find is various comments around the idea that because the oxidation state of P in H3P04 is +5 it can’t be oxidised further and so therefore can’t act as an oxidant.  This does not make sense to me because if anything that would mean that it would very much be able to act as an oxidant (have the ability to accept electrons) but would not be able to act as a reductant?

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Re: Why does phosphoric acid H3P04 not act as an oxidant?
« Reply #1 on: January 25, 2024, 05:32:40 AM »
Quote
On googling this all I can find is various comments around the idea that because the oxidation state of P in H3P04 is +5 it can’t be oxidised further and so therefore can’t act as an oxidant. 

That is wrong, its opposit. It must say it can't be used as an reductant.

If something works as an oxidant , it will be itself reduced, it gains electrons. This is theoretical  possible with phosphorous. From oxidation state 5 it can be down to 3 or even to 0 or -3.
In opposit if something works as an reductant then it donate electrons. Itself it will be oxidised.

Offline lloyd709

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Re: Why does phosphoric acid H3P04 not act as an oxidant?
« Reply #2 on: January 25, 2024, 07:58:02 AM »
Quote
On googling this all I can find is various comments around the idea that because the oxidation state of P in H3P04 is +5 it can’t be oxidised further and so therefore can’t act as an oxidant. 

That is wrong, its opposit. It must say it can't be used as an reductant.

If something works as an oxidant , it will be itself reduced, it gains electrons. This is theoretical  possible with phosphorous. From oxidation state 5 it can be down to 3 or even to 0 or -3.
In opposit if something works as an reductant then it donate electrons. Itself it will be oxidised.

That's what I thought.  Thanks for confirming.  There seems to be quite a bit of miss information about it around.  My text book states "Phosphoric acid does not act as an oxidant" which may be correct (it might be that while it theoretically could it just doesn't under normal circumstances) but my book doesn't give any further information (which is why I googled it and got even more confused).

Offline Borek

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Re: Why does phosphoric acid H3P04 not act as an oxidant?
« Reply #3 on: January 25, 2024, 08:52:19 AM »
My text book states "Phosphoric acid does not act as an oxidant" which may be correct (it might be that while it theoretically could it just doesn't under normal circumstances)

More or less what you wrote - it can, but it is quite lazy ;)

I have some vague recollection of processes in which H3PO4 is an oxidizer, but it is probably due to the selection of products that shift the equilibrium to the right. Compared to nitric (or even sulfuric) acid phosphoric is just way too inert to have practical applications as an oxidizer.
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