A 31.27mL volume of sodium hydroxide at 0.167molL1 concentration was used to neutralize a 22.5mL volume of AQUEOUS H3PO4. What is [H3PO4](aq)?

1 Answer
Aug 26, 2016

H3PO4(aq)+2NaOH(aq)Na2HPO4(aq)

Explanation:

Note the stoichiometry. You reach a stoichiometric endpoint at biphosphate, HPO24, NOT PO34.

Moles of sodium hydroxide = 31.27×103L×0.167molL1 = 5.22×103mol.

There were thus 5.22×103mol2 with respect to H3PO4 in the volume of 22.5mL.

Molarityphosphoric acid = 5.22×103mol2×122.5×103L 0.1molL1 with respect to phosphoric acid.