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deep0199

Acid/Base?

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Given this equation:

PH2O2-(aq) + OH-(aq) --> PHO32-(aq) + H2(g)

 

How do I determine whether the OH- is acting as an acid or base? Any explanations will be greatly appreciated.

 

Thanks in advance.

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What's the counter ion? Na+ or K+ probably.

 

PH2O2Na + NaOH ---> PHO3Na2 + H2

 

I'd say it's acting like an acid since it's loosing it's H+. Though I haven't delt with this kinda question before so It be nice if someone could confirm this.

 

**Though on the other hand it's not really acting like a Lewis acid since there really isn't any net gain or loss of electrons for the O or the H or the P. Really all that's happening is the OH swapping one covalent bond to it's hydrogen for one to the Phosphorus. P and H have almost identical electronegativities with P being higher but insignificantly so.**

 

Acid would be my answer though.

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This doesn't look like a clear acid/base reaction to me, but more like an oxidation /reduction reaction. The phosphorus is being oxidized while the hydrogens are being reduced to form hydrogen gas. Broken down the reactions probably look like a substitution reaction followed by an acid/base reaction:

 

H2PO2- + OH- --> H3PO3- + H-

 

Here the OH is acting like a lewis base (nucleophile) by donating its lone pair to form a bond with the hypophosphite (the lewis acid/electrophile). The hydride ion acts as a leaving group in this substitution reaction.

 

Now comes the acid/base part of the reaction:

H3PO3- + H- --> H2PO32- + H2

 

Here the phosphorous acid acts as the (Brønsted) acid and the hydride ion acts as the (Brønsted) base.

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H2PO2- + OH- --> H3PO3- + H-

 

Here the OH is acting like a lewis base (nucleophile) by donating its lone pair to form a bond with the hypophosphite (the lewis acid/electrophile). The hydride ion acts as a leaving group in this substitution reaction.

 

This is unbalanced. There is an extra hydrogen on the right side.

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Ah, thanks for noticing the error. Here are the corrected equations:

 

H2PO2- + OH- --> H2PO3- + H-

 

H2PO3- + H- --> HPO32- + H2

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