What is the process for determining empirical formulas from percentage composition?

The process for determining empirical formulas from percentage composition involves converting percentages to masses, then to moles, and finally simplifying the mole ratio.

To start, you need to know the percentage composition of each element in the compound. This information is usually provided in the problem. The first step is to convert these percentages into grams. This is done by assuming you have 100g of the compound, so the percentage directly translates into a mass in grams. For example, if a compound is 40% carbon, you would have 40g of carbon in a 100g sample.

Next, you need to convert these masses into moles. This is done by dividing the mass of each element by its atomic mass. The atomic mass can be found on the periodic table. For example, the atomic mass of carbon is approximately 12, so you would divide 40g by 12 to get the number of moles of carbon.

Once you have the number of moles of each element, you need to find the simplest whole number ratio of these moles. This is done by dividing each number of moles by the smallest number of moles calculated. For example, if you calculated 3.33 moles of carbon and 5 moles of hydrogen, you would divide both by 3.33 to get a ratio of 1:1.5. Since empirical formulas must be in whole numbers, you would then multiply these numbers by 2 to get a ratio of 2:3.

This ratio is the empirical formula of the compound. In this example, the empirical formula would be C2H3. This process can be used to determine the empirical formula of any compound from its percentage composition.