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pH of weak acid after neutralizing

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yene:
Hi guys,

Consider a situation where a weak acid (H3PO4 in my case) is used to neutralize a diluted strong basic solution (NaOH in water).

So I know that the H3PO4 partially dissociates into H+ and H2PO4(knowing the molarity of H3PO4 and Ka of the reaction, I know that 14.7 M of H3PO4 dissociates into 0.3M of H+).

So here's my question: once the OH- ions are neutralized by those H+ ions, does the H3PO4 in the solution dissociate again in order to maintain equilibrium within that dissociation reaction? Since the new solution will have H3PO4 ions and no H+ ions, I'm wondering if there's a sort of 'Le Chatalier' effect that makes the H3PO4 're-dissociate' into some more H+ ions.

This is a concern to me because I don't want to add enough H3PO4 to neutralize the OH- solution and then have it dissociate into even more H+ ions, thus giving me an overly acidic solution.

Any help is super appreciated.

Thanks guys.

yene:
Perhaps the easier question is this:

If i have an excess of [OH-] ions in a solution, and use a weak acid to neutralize it, will the weak acid eventually completely dissociate?

My logic is the following:
At first, the weak acid would only partially dissociate, but all of the dissociated H+ ions would get totally consumed by neutralizing OH- ions. So to maintain equilibrium, the weak acid would partially dissociate again, and again all of the dissociated H+ ions would get totally consumed, and this cycle would continue until the weak acid is totally dissociated.

chenbeier:
Phosphoric acid has 3 dissocation steps.

H3PO4 to H2PO4- to HPO42- to PO43-

So first Phosporic acid will neutralized to the first step dihydrogen phosphate, if all H+ consumed it will  neutralize to hydrogen phosphate and finally to phosphate.
Regarding the pKs values will be phosphate in alkaline pH.

Borek:
All forms of the dissociated acid are always present in the solution in equilibrium concentrations.

1M phosphoric acid contains approximately 0.92 M H3PO4, 0.081 M H2PO4-, 6.3×10-8 M HPO42- and 3.5×10-19 M PO43-. Neutralizing the acid will change these values shifting the maximum fraction towards higher charge anions., around pH 13-14 the situation will reverse - solution will be dominated by PO43- and H3PO4 will be present in 10-19 M concentrations.

yene:
Thanks for those replies, but in response:

The Ka for H2Po4 dissociation and HPO4 dissociation is way lower than that of the H3PO4 dissociation, therefore my understanding is that those subsequent reactions are negligible in this situation regarding Hydrogen production.

So just neglecting those subsequent reactions for now: in a solution with excess OH-, does the weak acid eventually fully dissociate?

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