Chapter 4, Problem 62QAP

Ten mL of concentrated H₃PO₄ (91.7% by mass, $d=1.69\text{g}/\text{mL}$) was accidentally poured into a beaker containing 20.0 g of NaOH. Not all the NaOH was consumed. How many grams of NaOH were left unreacted? The equation for the reaction is

${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}\left(aq\right)+{\text{3OH}}^{-}\left(aq\right)\to {\text{3H}}_{\text{2}}\text{O}+{\text{PO}}_{\text{4}}{}^{\text{3}-}\left(aq\right)$