# Empirical formula

{{#invoke:Hatnote|hatnote}} In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound.[1] A simple example of this concept is that the empirical formula of hydrogen peroxide, or H2O2, would simply be HO.

An empirical formula makes no mention towards arrangement or number of atoms. It is standard for a lot of ionic compounds, like CaCl2, and for macromolecules, such as SiO2.

The molecular formula on the other hand shows the number of each type of atom in a molecule, also the structural formula shows the arrangement of the molecule. It is possible for different types of compounds to have equal empirical formulas.

## Calculation

Suppose you are given a compound such as methyl acetate, a solvent commonly used in paints, inks, and adhesives. When methyl acetate was chemically analyzed, it was discovered to have 48.64% carbon (C), 8.16% hydrogen (H), and 43.20% oxygen (O). For the purposes of determining empirical formulas, we assume that we have 100 g of the compound. If this is the case, the percentages will be equal to the mass of each element in grams.

Step 1
Change each percentage to an expression of the mass of each element in grams. That is, 48.64% C becomes 48.64 g C, 8.16% H becomes 8.16 g H, and 43.20% O becomes 43.20 g O.
Step 2
Convert the amount of each element in grams to its amount in moles.
${\displaystyle \left({\frac {48.64{\mbox{ g C}}}{1}}\right)\left({\frac {1{\mbox{ mol }}}{12.01{\mbox{ g C}}}}\right)=4.049\ {\text{mol}}}$
${\displaystyle \left({\frac {8.16{\mbox{ g H}}}{1}}\right)\left({\frac {1{\mbox{ mol }}}{1.008{\mbox{ g H}}}}\right)=8.095\ {\text{mol}}}$
${\displaystyle \left({\frac {43.20{\mbox{ g O}}}{1}}\right)\left({\frac {1{\mbox{ mol }}}{16.00{\mbox{ g O}}}}\right)=2.7\ {\text{mol}}}$
Step 3
Divide each of the found values by the smallest of these values (2.7)
${\displaystyle {\frac {4.049{\mbox{ mol }}}{2.7{\mbox{ mol }}}}=1.5}$
${\displaystyle {\frac {8.095{\mbox{ mol }}}{2.7{\mbox{ mol }}}}=3}$
${\displaystyle {\frac {2.7{\mbox{ mol }}}{2.7{\mbox{ mol }}}}=1}$
Step 4
If necessary, multiply these numbers by integers in order to get whole numbers; if an operation is done to one of the numbers, it must be done to all of them.
${\displaystyle 1.5\times 2=3}$
${\displaystyle 3\times 2=6}$
${\displaystyle 1\times 2=2}$

Thus, the empirical formula of methyl acetate is Template:Chem. This formula also happens to be methyl acetate's molecular formula.