# Question #c5c01

Jan 16, 2014

Heptane has a formula of ${C}_{7} {H}_{16}$ which is and empirical formula ratio of ${C}_{n} {H}_{2 n + 2}$, this is true for all of the hydrocarbons that end in -ane.

First find the molar mass (gram formula mass) of the molecule using the atom values and masses from the periodic table.

C has a mass of 12.01 amu (mass from the periodic table)
H has a mass of 1.01 amu

There are 7 carbon atoms and 16 hydrogen atoms in this molecule.

C 6 x 12.01 = 72.06
H 17 x 1.01 = 17.17

72.06 + 17.17 = 89.03 g/mole

Now find the percent breakdown by comparing the mass of each element to the mass of the molecule.

72.06 / 89.03 = 0.8093 or 80.9%
17.17 / 89.03 = 0.193 or 19.3%

Heptane is 80.9% Carbon and 19.3% Hydrogen.

Here is a YouTube videos on determining percent composition and gram formula mass.