In labs today — as well as in the study of chemistry — you are much more likely to bump into the molecular formula for a compound rather than the empirical formula. The reason for this is that we now know that individual molecules tend to be more complex than the smallest whole number ratio of atoms within them.
Going by empirical formula alone, we would also end up with different compounds sharing the same formula, which isn’t very useful when trying to categorize chemical properties. The total mass of a molecule could be much larger than its empirical formula would suggest.
Table salt is a very convenient compound to measure when it comes to empirical formula because it contains exactly one sodium and one chlorine atom per molecule. Not all compounds divide so perfectly, and knowing the simplest ratio of mass inside the molecule may not tell us exactly what is actually a single molecule.
What Molecular Formulas Tell Us About a Compound
Let’s take two chemical compounds, acetylene and benzene, which share the same ratios and same empirical formula: CH, which is one hydrogen atom per one carbon atom. Compounds will share an empirical formula when the chemical formula of one is a multiple of the other. In this case the chemical formula for acetylene is C2H2 while benzene’s is C6H6.
Although they have the same basic makeup, one molecule of benzyne has three times the number of atoms and three times the molar mass as an acetylene molecule. They are both classified as hydro-carbons but have different uses.
- Acetylene is used as a fuel for extremely high heat applications like welding.
- Benzene is considered too toxic when burned, and is instead used for industrial plastic production.
If chemists or industries were to assume that materials like acetylene and benzyne were actually the same compound based solely on their empirical formula, it could lead to flaws in the products they attempt to make, or even worse, it could lead to serious danger when a welder uses a highly toxic compound as fuel. Categorizing all these known chemicals correctly can literally save lives.
