Question

Balance the equation under basic conditions Au + CN‒ + O2 → Au(CN)4 ‒ + OH‒

Answer 1

Au + CN^- + O₂ ----------> Au(CN)₄^- + OH-

0                   0                    +3            -2

Oxidation Half Reaction               Reduction Half Reaction

1. Au + CN^- --------> Au(CN)₄^-                    O₂ ----------> OH^-

2. Balance all other atoms except O and H

Au + 4 CN^- ---------> Au(CN)₄^-                   O₂ --------> OH^-

3. To Balance Oxygen atoms add OH- ions in basic medium.

Au + 4 CN^- ------------> Au(CN)₄^-              O2 --------> OH^- + OH^-

4. To balance hydrogen atoms add H2O molecules in basic medium.

Au + 4 CN^- ----------> Au(CN)₄^-              O₂ + 2 H₂O ---------> 4 OH^-

5. To balance charges add electrons

Au + 4 CN^- --------> Au(CN)₄^- + 3 e       O₂ + 2 H₂O + 4 e ---------> 4 OH^-

6. To equalise electrons in both half reaction,

do OHR * 4 and RHR * 3

4 Au + 16 CN^- ----------> 4 Au(CN)₄^- + 12 e         3 O₂ + 6 H₂O + 12 e -----------> 12 OH^-

7. Add both half reactions to get balanced redox reaction.

4 Au + 16 CN^- + 3 O₂ + 6 H₂O -------> 4 Au(CN)₄^- + 12 OH^-