Balancing redox equations
reactants: Cu, NO3
To balance a redox equation, you need to follow a few steps:
Step 1: Assign oxidation numbers
First, you need to determine the oxidation numbers (or oxidation states) of the elements in the reaction. In this case, we have Cu and NO3.
Copper (Cu) typically has an oxidation state of 0 in its standard state, and NO3 (nitrate) is a polyatomic ion with an oxidation number of -1. However, these oxidation numbers can change during a chemical reaction.
Step 2: Identify the redox reaction
Next, identify which atoms are undergoing oxidation (losing electrons) and which are undergoing reduction (gaining electrons).
In this case, copper (Cu) is being oxidized because its oxidation number is increasing, while nitrate (NO3) is being reduced because its oxidation number is decreasing.
Step 3: Balance the atoms
Now, balance the atoms in the equation. Start by balancing all atoms except oxygen and hydrogen.
In this case, there is only one copper atom on both sides of the chemical equation, so it is already balanced.
However, the nitrate ion (NO3-) has one nitrogen atom and three oxygen atoms. To balance the nitrogen, place a coefficient of 2 in front of NO3-, giving you 2NO3-.
Step 4: Balance oxygen atoms
Balance the oxygen atoms by adding water (H2O) molecules to the side that needs oxygen.
In this case, there are six oxygen atoms on the right side (2NO3-) but none on the left side. So, you need to add three water molecules (H2O) on the left side to balance the equation. This gives you:
Cu + 2NO3- + 3H2O
Step 5: Balance hydrogen atoms
Next, balance the hydrogen atoms by adding H+ ions to the side that needs hydrogen.
In this case, there are six hydrogen atoms on the left side (3H2O) but none on the right side. So, you need to add six H+ ions on the right side. This gives you:
Cu + 2NO3- + 3H2O → Cu2+ + 2NO3- + 6H+
Step 6: Balance charges with electrons
Now, we balance the charges using electrons (e-). In this case, the copper (Cu) is being oxidized, so it loses two electrons. The nitrate ion (NO3-) is being reduced, so two electrons are gained by each NO3-.
To balance the charges, add two electrons (2e-) to the left side of the equation:
Cu + 2NO3- + 3H2O → Cu2+ + 2NO3- + 6H+ + 2e-
Step 7: Cancel out the species
Finally, cancel out the species that are the same on both sides of the equation. In this case, you can cancel out the nitrate ions (NO3-) on both sides, giving you the balanced equation:
Cu + 3H2O → Cu2+ + 6H+ + 2e-
This balanced equation represents the redox reaction between copper and nitrate ions in an acidic solution.