Question

When balancing a redox reactions how would you know when adding the electrons if the other side is zero?

For example: Cu + NO3^- —> Cu^2+ + NO

For NO3: NO3^- + 4H+ +5e —-> NO + 2H2O

How would I know that I have to add 5e when the other side doesn’t have any charge written on them? Would I assume that 2H2O is ^-2. But doesn’t that mean NO is ^-2 also since it’s oxygen?? I don’t get it

Answer 1

You would actually add 3 electrons to the left side.

Step-by-step explanation:

NO3^- has a charge of -1. When balanced in an acidic solution, there are 4H+ on the left side of the equation as well. This means the overall charge on the left side is +3 (4 hydrogen ions with a +1 charge = a +4 charge but the -1 charge from NO3^-1 must be added as well). The right side has an overall charge of 0 because there are no charges written above the compounds. H2O is a neutral molecule. In this case, NO is also a neutral molecule because there is no charge written above it to make it an ion. If the left side has a charge of +3 and the right has a charge of 0, 3 electrons must be added to the left to get both sides to have an overall charge of 0.