Video Transcript
Caffeine has the chemical formula C₈H₁₀N₄O₂. 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 molecule. And, we express it in the simplest whole-number ratios. The chemical formula for caffeine given in the problem is a molecular formula, which is a chemical formula that tells us the number of atoms of each element per molecule.
As an example, let’s take a 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. This is not the simplest whole-number ratio to express this amount of atoms. The simplest whole-number ratio is one to one. Which we can get by dividing by two, which is why the empirical formula for hydrogen peroxide is just HO.
Now, let’s find the empirical formula for caffeine. We need to express this chemical formula in the simplest whole-number ratios. We know it’s not in the simplest whole-number ratios right now, because everything is divisible by two. If we divide by two, we’ll get C₄H₅N₂O. Which is now expressing this chemical formula in the simplest whole-number ratios because it’s not divisible by anything else. So, C₄H₅N₂O is the empirical formula for caffeine.
