Determining the empirical formula of a hydrocarbon requires knowing the mass and the atomic weight of each element in a compound. While the atomic weights can be gained from a periodic table, the masses must be measured or provided in the given problem statement. If you are given percentages rather than masses, assume that there are 100 grams and use the percentages to determine the starting mass.
- Record the atomic weights of hydrogen and carbon
Record the atomic weights of hydrogen and carbon from the periodic table. In a hydrocarbon, these are the only two elements involved.
- Divide the given masses by the atomic weights
Divide the masses of the elements by their atomic weights to convert to moles. One mole will be equal to the atomic weight.
- Divide the amount of moles to get the factors
Divide each element's number of moles by the smallest number of moles. For example, if there are .250 moles of hydrogen and .500 moles of carbon, divide both figures by .250. It may be necessary to round to the nearest whole number.
- Add the calculated values to the elements
Take the calculated values from the previous step, and insert them into the formula. For example, from the previous step, there will be one hydrogen and two carbon. This produces an empirical formula of C2H.