# Question a455e

Oct 5, 2016

86.35%

#### Explanation:

First write the molecular formula:
$C {F}_{4}$

To find the percentage (by mass) of fluorine in the compound, we first find the mass of the whole molecule. Note that we aren't given any numbers such as 1kg or 5g, and this is because we are supposed to use the relative atomic masses (as found on your periodic table)

Molecular Mass of $C {F}_{4} = 1 \cdot 12.01 + 4 \cdot 19.00$
$= 88.01$

Then find the molecular Mass of $F$ within the molecule. Just do this by counting the number of fluorine atoms in the molecule (4):
Molecular Mass of $F = 4 \cdot 19.00$
$= 76.00$

Then because we're asked for a percentage, we just divide the mass of fluorine by the mass of the whole thing and multiply by 100%

Mass percentage of fluorine = 76.00 / 88.01 * 100%
=86.35%#