Question

The standard electrode potential corresponding to the reaction Au³⁺(aq) + 3e^- → Au(s) is 1.5 V. Predict if gold can be dissolved in 1M HCl solution and on passing hydrogen gas through gold salt solution, metallic gold will be precipitated or not.

Answer 1

Consider the half reaction, 

2H⁺(aq) + 2e^– → H₂(g); E° = 0.0V

Au³⁺(aq) + 3e^– → Au(s); E° = 1.50V

Since E° (1.50V) for (Au³⁺/Au) is higher than that H⁺/-\(\frac{1}{2}\)H₂ (0.0V), therefore, Au³⁺ can be more easily reduced than H⁺ ions Au³⁺ can be reduced to Au metal by H₂ but H⁺ cannot oxidize metallic gold to Au³⁺ ions. In other words, metallic gold does not dissolve in 1M HCl instead H₂ gas can reduce gold salt to metallic gold.