percent+composition

Percent Composition is defined as the ratio of the mass of all the atoms of a given element to the mass of its parent compound, reported as a percentage:

% of element X = (mass of element X in the compound) / (molar mass of compound) x 100

To calculate percent composition for a specific element in a compound, follow these steps:
 * 1) Calculate the formula weight of the compound.
 * 2) Calculate the mass of just the element in question in the compound.
 * 3) Divide the element's mass by the formula weight, and multiply by 100.

Here is an example: calculate the percent by mass of silver in silver oxide.

Solution: silver oxide has a compound formula of Ag 2 O.

Its formula weight is calculated:

Ag 2 x 107.868 = 215.736 __O 1 x 15.999 = 15.999__ f.w. = 231.735 amu

The percent of silver is then calculated:

% Ag = (215.736 / 231.735) x 100 = 93.10 % Ag

The following link is an online percent composition calculator. Here is another that shows composition graphically.

Try this worksheet (page 2) for practice: