Acid/Base?

[deep0199]

Given this equation:

PH₂O₂^-(aq) + OH^-(aq) --> PHO₃^2-(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.

[Bluenoise]

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.

[Yggdrasil]

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^- --> H₂PO₃^2- + H₂

 

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

[Bluenoise]

 

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.

[Yggdrasil]

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

 

H₂PO₂^- + OH^- --> H₂PO₃^- + H^-

 

H₂PO₃^- + H^- --> HPO₃^2- + H₂