11852 13 Chloroauric acid, HAuCl4, is an orange solid that is used widely in gold refining. During World War II, the Hungarian chemist George de Hevesy dissolved two gold Nobel Prize medals in a mixture of concentrated nitric and hydrochloric acids to prevent the Germans from confiscating them. Later the medals were reconstructed from the dissolved chloroauric acid and returned. (a) The reaction between gold, concentrated hydrochloric acid and concentrated nitric acid produces chloroauric acid, nitrogen(IV) oxide and water. Write the equation for this reaction. [2] (b) Gold is extracted from recycled electronic materials by reaction with chlorine and hydrochloric acid, forming chloroauric acid. Elemental gold is recovered by electrolysis of chloroauric acid. 2Au  +  3Cl2  +  2HCl  →  2HAuCl4 (i) Deduce the oxidation state of gold in chloroauric acid. [1] (ii) With reference to oxidation numbers, explain why this is a redox reaction. [3] 11852 [Turn over (c) When heated, chloroauric acid forms gold(III) chloride and hydrogen chloride gas. The bonding in gold(III) chloride is considered to be covalent. (i) Suggest, in terms of electronegativity, why the bonding in gold(III) chloride is covalent. [1] (ii) Describe the chemical test for hydrogen chloride gas. [2]