# Question b9857

Jan 16, 2014

For each element, you divide the total mass of its atoms by the empirical formula mass and multiply by 100.

#### Explanation:

EXAMPLE

What is the percent composition of a compound with the empirical formula $\text{CH"_2"O}$?

Solution

Step 1: Find the masses of the individual atoms.

$\text{C = 12.01 u}$
$\text{H = 1.008 u}$
$\text{O = 16.00 u}$

Step 2: Find the total mass of each atom in the formula.

$\text{1 C = 12.01 u}$
$\text{2 H = 2.016 u}$
$\text{1 O = 16.00 u}$

Step 3: Find the total mass of all the atoms in the formula.

$\text{CH"_2"O = (12.01 + 2.016 + 16.00) u = 30.03 u}$

Step 4: Find the mass percent of each atom.

"mass %" = "mass of atom"/"total mass" × "100 %#

$\text{mass % C" = (12.01 color(red)(cancel(color(black)("u"))))/(30.03 color(red)(cancel(color(black)("u")))) × "100 %" = "40.00 %}$

$\text{mass % H" = (2.016 color(red)(cancel(color(black)("u"))))/(30.03 color(red)(cancel(color(black)("u")))) × "100 %" = "6.714 %}$

$\text{mass % O" = (16.00 color(red)(cancel(color(black)("u"))))/(30.03 color(red)(cancel(color(black)("u")))) × "100 %" = "53.29 %}$

$40.00 + 6.714 + 53.29 = 100.00$