I have the following question in a chemistry homework:

Calculate the $\mathrm{pH}$ of a solution made by dissolving $\pu{113 g}$ of sodium phosphate in enough water to make a solution with a final volume of $\pu{475 mL}$. Find the equilibrium concentration of all species present in this solution.

It shouldn't be that hard of a problem, but my teacher really doesn't explain well at a distance (with the COVID-19 situation). I have found that it dissociates into $\ce{NaOH}$ and $\ce{H3PO4}$ when in water: $$\ce{Na3PO4(s) + 3H2O(l) → 3NaOH(aq) + H3PO4(aq)}$$

But I don't really know what to do next...

Thanks in advance!

  • $\begingroup$ You do not think it can be strongly acidic and strongly alkalic at the same time, do you ? Google 3 equilibrium dissociation reactions of phosphoric acid. $\endgroup$ – Poutnik Apr 30 '20 at 15:30
  • $\begingroup$ No of course not, but if $Na_3PO_4$ dissociates and just the $PO_4$ ion reacts with water, it could make $HPO_4$, $H_2PO_4$ or $H_3PO_4$, right? $\endgroup$ – Thibaut B. Apr 30 '20 at 15:50
  • $\begingroup$ Yes, right, but you need to quantify that. Technote: If you use mhchem MathJax extension, you can Write formulas as \$\ce{H3PO4}\$ what will look like $\ce{H3PO4}$ $\endgroup$ – Poutnik Apr 30 '20 at 15:52
  • $\begingroup$ See phosphoric acid section acidic properties. $\endgroup$ – Poutnik Apr 30 '20 at 16:02
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    $\begingroup$ Sorry, it is not an easy problem. If she really means "find the equilibrium concentration of all species present in this solution." $\endgroup$ – M. Farooq Apr 30 '20 at 21:29