Sodium peroxide has the formula Na₂O₂. What is its empirical formula?
An empirical formula is a chemical formula that tells us the relative number of atoms for each element in a compound, and we express it in the simplest whole-number ratios. The chemical formula for sodium peroxide given in the problem is a molecular formula, which tells us the number of atoms of each element per molecule. As an example, let’s look at hydrogen peroxide. Hydrogen peroxide has the molecular formula H₂O₂. Because there are two hydrogen atoms and two oxygen atoms in a molecule of hydrogen peroxide. The empirical formula for hydrogen peroxide is simply HO.
While there are two hydrogen atoms for every two oxygen atoms in a molecule of hydrogen peroxide. Two to two is not the simplest whole-number ratio that we could express this in because it’s divisible by two. The simplest whole-number ratio is one to one, which is what we use in the empirical formula.
Now, let’s find the empirical formula for sodium peroxide. Which will be this chemical formula expressed in the simplest whole-number ratios. Right now, we don’t have the simplest whole-number ratio because everything is divisible by two. If we divide by two, we’ll get NaO, which is now the simplest whole-number ratio. So, NaO is the empirical formula for sodium peroxide.