Balance the equation below by adding stoichiometric coefficients

Question

Au + HNO3 + HCl --> HAuCl4 + NO2 + H2O

What is the function of HCl?

Answer 1

Au goes from 0 to +4 oxidation number (it is being oxidized)

N goes from +5 to +4 oxidation number (it is being reduced)

Oxidation half reaction:

Au + HCl ==> HAuCl₄

Au + 4HCl ==> HAuCl₄ .. balanced for Au and Cl

Au + 4HCl ==> HAuCl₄ + 3H⁺ .. balanced for Au, Cl and H

Au + 4HCl ==> HAuCl₄ + 3H⁺ + 3e- .. balanced oxidation reaction

Reduction half reaction:

HNO₃ ==> NO₂

HNO₃ ==> NO₂ + H2O .. balanced for N and O

HNO₃ + H⁺ ==> NO₂ + H2O .. balanced for N, O and H

HNO₃ + H⁺ + e- ==> NO₂ + H2O .. balanced reduction reaction

Au + 4HCl ==> HAuCl₄ + 3H⁺ + 3e-

3HNO₃ + 3H⁺ + 3e- ==> 3NO₂ + 3H2O

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Au + 4HCl + 3HNO₃ ==> HAuCl₄ + 3NO₂ + 3H2O .. BALANCED REDOX EQUATION