Question

How do you balance

Cu + NO3-1 --> Cu+2 + NO2

Answer 1

Given reaction is Cu + NO₃^- ----> Cu²⁺ + NO₂

1) Write half reactions

Oxidation: Cu -----> Cu²⁺ + 2e-
Reduction: NO₃^- + e- -----> NO₂

(2) Balance each half-reaction with respect to atoms first, then with respect to electrons.

Oxidation: Cu -----> Cu²⁺ + 2e-

Reduction: 2NO₃^- + 2e- -----> 2NO₂

(3) Balance Oxygen atoms by adding H₂O and balance Hydrogen atoms by adding H+

Oxygen atoms in the reduction step that are not balanced. Then, add as many H₂O molecules on the right as are needed to balance the total oxygens on the left.

Then add H+ ions on the left side of the arrow to balance the number of hydrogen atoms that were introduced with the H₂O molecules.

Oxidation: Cu -----> Cu²⁺ + 2e-

Reduction: 2NO₃^- + 2 e- + 4H+ -----> 2NO₂ + 2H₂O

(4) Add the two half-reactions together cancelling the electrons which are now equal on each side of the arrow

Cu -----> Cu²⁺ + 2e-

2NO₃^- + 2 e- + 4H+ -----> 2NO₂ + 2H₂O
------------------------------------------------------------------------------

Cu + 2NO₃^- + 4H+ -----> Cu²⁺ + 2NO₂ + 2H₂O

This is the balanced equation.