Gold has always been a highly prized metal, widely used from the beginning of hi

Question

Gold has always been a highly prized metal, widely used from the beginning of history as a store of value. It doesn't rust like iron and doesn't become tarnished like silver. It is so chemically inert that it won't react even with the strongest concentrated acids. But it can be dissolved in aqua regia a fresh-prepared mixture of concentrated HNO3 and HCl (1:3). 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 out of the acid 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 below. Add the stoichiometric coefficients to the equation to balance it. Au(s) + HNO,(aq) + HCI(aq) HAuCI4(aq) + NO,W-H20(1)

Explanation / Answer

Au(s)+HNO3(aq)+HCl(aq) ------->HAuCl4(aq)+NO2(g)+ H2O(l)

since there are 4 Cl atoms in HAuCl4, write 4 in front of HCl. Next balances the oxygen atoms which can be done by addition of 3 to HNO3 and 3 to NO2. this gives rise to 7 H atoms on reactants side. One H is there in HAuCl4. hence 6 Hydrogen atoms are left. This is done by addition of 3 in front of H2O. The balanced equation is

Au(s)+ 3HNO3+4HCl --------->HAuCl4+ 3NO2+3H2O

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