Question

What is the product formed when gold is dissolved in aqua regia?

• A. $H_{3}AuC{l}_2{O}_2$
• B. $HAuC{l}_4$
• C. $H_{2}AuC{l}_4$
• D. $H_{2}AuCl{O}_2$

Answer 1

Answer: (B)

$HAuC{l}_4$

The following reactions represent reaction between gold and Aqua region oxidizing behaviour of $HN{O}_3$

$AU\left(s\right)$ $+$ ${3NO}_3^{-}\left(aq\right)$ $+$ ${6H}^{+}\left(aq\right)$ $\rightleftharpoons$ ${Au}^{3+}\left(aq\right)$ $+$ $3N{O}_2\left(g\right)$ $+$ $3H_{2}O\left(s\right)$

Chloride ions of $HCl$ forms Coordination Complex with gold

${Au}^{3+}\left(aq\right)$ $+$ $4HCl\left(aq\right)$ $\rightleftharpoons$ $AuC{l}_4$

$H^{+}$ $+$ ${AuCl}_4^{-}$ $\rightleftharpoons$ $HAuC{l}_4$

Hence the product is $HAuC{l}_4$