Question

Gold dissolves in aqua regia to give:

• A. $H\left[AuC{l}_4\right]$
• B. $AuN{O}_3$
• C. $H_2\left[AuC{l}_6\right]$
• D. $Au(N{O}_3{)}_3$

Answer 1

The correct option is A $H\left[AuC{l}_4\right]$

Aqua regia is a strong acid which is formed by mixing concentrated nitric acid and concentrated hydrochloric acid in a 1:3 ratio.

When gold is dissolved in aqua regia, the following reaction occurs:
$Au{}_{\left(s\right)}+3N{O}_3^{-}{}_{(aq.)}+6H^{+}{}_{(aq.)}\rightleftharpoons A{u}^{3+}{}_{(aq.)}+3N{O}_2{}_{\left(g\right)}+3H_{2}O{}_{\left(l\right)}$

$A{u}_{(aq.)}^{3+}+C{l}_{(aq.)}^{-}\rightleftharpoons [AuC{l}_4{]}_{(aq.)}^{-}$

The formed complex reacts with a proton to form chloroauric acid.

$H^{+}+[AuC{l}_4{]}^{-}⟶H[AuC{l}_4]$