Question 4 of 20 >
Gold has always been a highly prized metal, and it has been widely used from the beginning of history as a store of value. It
does not rust like iron and does not become tarnished like silver. It is so chemically inert that it will not react with even the
strongest concentrated acids. But it can be dissolved in aqua regia, a fresh-prepared mixture of concentrated $HNO_3$ and HCl in a
1:3 ratio.
When Germany invaded Denmark in World War II, the Hungarian chemist George de Hevesy dissolved the gold Nobel Prizes of
Max von Laue and James Franck in aqua regia to prevent the Nazis from stealing them. He placed the jar with the solution on a
shelf in his laboratory and, after the war, precipitated the gold from the acid solution and returned it to the Royal Swedish
Academy of Sciences and the Nobel Foundation, who recast the medals and again presented them to Laue and Franck.
The unbalanced equation for the reaction of gold with aqua regia is given. Add the stoichiometric coefficients to the equation to
balance it.
equation: Au(s) + $HNO_3$(aq) + 4HCl(aq) ā $HAuCl_4$(aq) + $NO_2$(g) + $H_2O$(1)
What is the function of HCI?
It supplies chloride ions to form a complex ion with the oxidized gold.
ā It acts as an oxidizing agent.
ā It acts as a reducing agent.
