Chapter 4, Problem 60QAP

Gold metal will dissolve only in aqua regia, a mixture of concentrated hydrochloric acid and concentrated nitric acid in a 3:1 volume ratio. The products of the reaction between gold and the concentrated acids are AuCl₄^-(aq), NO(g), and H₂O. The equation for this reaction where HNO₃ and HCl are strong acids is

$\text{Au}\left(s\right)+{\text{4Cl}}^{-}\left(aq\right)+{\text{4H}}^{+}\left(aq\right)+{\text{NO}}_{\text{3}}{}^{-}\left(aq\right)\to {\text{AuCl}}_{\text{4}}{}^{-}\left(aq\right)+\text{NO}\left(g\right)+{\text{2H}}_{\text{2}}\text{O}$(a) What stoichiometric ratio of hydrochloric acid to nitric acid should be used?

(b) What volumes of 12 M HCl and 16 M are HNO₃ required to furnish the Cl^- and NO₃^- ions to react with 25.0 g of gold?