AA Sapling Learning makamilan leaming Gold has always been a highly prized metal
ID: 511210 • Letter: A
Question
AA Sapling Learning makamilan leaming 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 agua regia to prevent the Nazis from stealin 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. Tip: If you need to clear your work and reset the equation, click the button that looks like two red arrows. What is the function of HCI? O It supplies chloride ions to form a complex ion with the oxidized gold. O It acts as a reducing agent O t acts as an oxidizing agent.Explanation / Answer
The balanced chemical equation as follows:
Reactant side only one chlorine atom is present where as in product side four chlorine atoms are present.
To balance the chlorine atoms take coefficient 4 before HCl.
Au(s) + HNO3(aq) + 4HCl(aq) ------> HAuCl4(aq) + NO2(g) + H2O(l)
To balance oxygen and hydrogen take coefficient 3 before HNO3 and NO2 and H2O.
Au(s) + 3HNO3(aq) + 4HCl(aq) ------> HAuCl4(aq) + 3NO2(g) + 3H2O(l)
Hence equation is balanced.
Oxidation: increasing oxidation number is called oxidation.
Reduction: Decreasing oxidation number is called reduction.
Oxidising agent: It self reduced.
Reducing agent: It self oxidised.
Reactant side oxidation numbers:
Au : 0
H : +1
O : -2
N : +5
Cl : -1
Product side oxidation numbers:
Au : +3
Cl : -1
O : -2
N : +4
H : +1
Here oxidation number of Au increases from 0 to +3
So Au is oxidised.
HCl neither oxidised nor reduced.
Hence the correct option is
It supplies Chloride ions to form a complex ion with the oxidised gold.