Balance the following skeletal equation, and identify the reducing and oxidizing reagent.
O2 (g) + NO (g) `->` NO3- (aq)
Hint: The pH of the resulting solution is lower than the pH of the initial solution.
You had an error in your question by listing the NO3- ion as a gas. As an ion, it exists in aqueous solution. We know from the pH information above that protons must be produced in the products since that would lower the pH. We can solve this via the half reaction method. Take each reagent and product pairing and balance them separately. Then add the two equations together to get the final balanced reaction.
Start with O2. The only product we can write for it is H2O since we are told that the product is aqueous.
O2 --> 2H2O
Now balance the hydrogens with protons in the reactants.
4H+ + O2 --> 2H2O
Now add electrons to balance the charge.
4e- + 4H+ + O2 --> 2H2O (1)
Now let's look at the other half of the equation.
NO --> NO3-
Balance the oxygens with water, the hydrogens with protons, and finally the charges with electrons, just like we did above. The steps are shown below.
2H2O + NO --> NO3-
2H2O + NO --> NO3- + 4H+
2H2O + NO --> NO3- + 4H+ + 3e- (2)
Now we multiply equation (1) by 3 and equation (2) by 4 to make each have the same total of electrons (12).
12e- + 12H+ + 3O2 --> 6H2O
8H2O + 4NO --> 4NO3- + 16H+ + 12e-
If we algebraically sum the two equations, the electrons will cancel each other out, as will 6 of the waters and 12 of the protons. The final chemical equation is shown below:` ` ` `
2H2O + 3O2 + 4NO --> 4NO3- + 4H+
This makes sense that there are protons in the products since we know that the pH of the products is lower (more acidic) than the reagents. The O2 is being reduced (it is the oxidizing agent) and the NO is being oxidized (it is the reducing agent).