If a compound is 86% carbon and 14% hydrogen by mass. What is the empirical formula for this compound?

1 Answer
Jun 17, 2014

The empirical formula is #CH_2#

The empirical formula contains the lowest whole number ratios of the elements in a compound. The term empirical refers to experimentation. So the percentage of the elements in a compound are experimentally derived (empirically determined).

For this example assume 100 grams of the compound. That means that we have 86 grams of carbon and 14 grams of hydrogen.

Next you want to convert these values to mole values since the subscripts denote mole values.

Take the mass of each element and divide by the molar mass of that element.
# 86 g C * (1mol C)/(12 g C) = 7.2 mol C#

#14 g H * (1mol H)/(1 g H) = 14 mol H#

The formula is #C_7.2H_14#

However, we are not finished, because the ratios(subscripts) must be in whole number ratios.
Divide the smaller value into the larger one and round to the nearest whole number which is #14/7.2#
This gives you 1.9 which is rounded to 2.

This means that we have one carbon atom for every two hydrogen atoms to give us a empirical formula of #CH_2#