Question

(4) (22 pts) Gold metal dissolves in aqua regia, which is a mixture of concentrated hydrochloric and concentrated nitric acids, but gold does not dissolve in either acid separately. (You may write net ionic equations in this problem.) (a) (6 pts) Write a balanced chemical equation for the reaction of gold and nitric acid to produce Au(aq) and nitric oxide. Calculate the standard emf (in V) for this reaction. Is this reaction spontaneous under standard conditions at 25°C? (b) (6 pts) Write a balanced chemical equation for reaction of gold and hydrochloric acid to produce AuCl(aq) and hydrogen gas. Calculate the standard emf (in V) for this reaction. Is this reaction spontaneous under standard conditions at 25°C? (c) (6 pts) Write a balanced chemical equation for reaction of gold and aqua regia, i.e., a mixture of nitric acid and hydrochloric acid, to produce AuCl(aq) and nitric oxide. Calculate the standard emf in V) for the reaction in (e). Is this reaction spontaneous under standard conditions at 25°C? (d) (4 pts) Concentrated nitric and hydrochloric acid have [H]> 1.0M (or [H:0*]> 1.0M). As [H') increases, the emf values for the reactions in (a), (b), and (c) all become more positive (or less negative) in value. From this information and your answers to (a), (b), and (c), briefly explain why aqua regia dissolves gold, but that the two separate acids do not. Useful Information Half-reaction E (V) 0.00 +0.79 +0.96 2 H*(aq) + 2 H2(g) NO3(aq) + 2 H(aq) + NO2(g) + H2O(1) NO;" (aq) + 4 H(aq) +36 - NO(g) + 2 H2O(1) AuCl4- (aq) + 3 - Au(s) +4 Cl(aq) HNO3(aq) + H+ (aq) + 2 NO(g) + H2O(1) NO2(aq) + H+ (aq) + HNO3(aq) Au(aq) + 36 - Au(s) +1.00 +1.00 +1.12 +1.50

Answer 1

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