Chemistry Notes

Percent Composition

In Review

The mole is an SI unit of

measure for amount of

particles

% Composition

The percent composition of

an element is the relative

amount of that element in a

compound.

% Composition

You find the percent composition of an element by dividing the element’s mass by the mass of the entire compound.

mass of element x 100

mass of compound

For example:

What is the % composition of carbon dioxide?

For example:

What is the % composition of carbon dioxide?

% Carbon = 12.011 g C x 100 = 27.3 % Carbon

44.009 g CO2

% Oxygen = 31.998 g O x 100 = 72.7 % Oxygen

44.009 g CO2

Try these…

What is the percent of each element

in phosphorus trichloride?

Try these…

What is the percent of each element

in phosphorus trichloride? PCl3

% Phosphorus = 30.974 g P x 100 = 22.6 % Phosphorus

137.333 g PCl3

% Chlorine = 106.359 g Cl x 100 = 77.4 % Chlorine

137.333 g PCl3

Try these…

If 20.0 grams Ca react completely with

16.0 grams of S to form a compound,

what is the percent of S?

Try these…

If 20.0 grams Ca react completely with

16.0 grams of S to form a compound,

what is the percent of S?

% Sulfur = 16.0 g S x 100 = 44.4 % Sulfur

36.0 g

% Water in a Hydrate

A hydrate is an ionic

compound with water as part

of its crystalline structure.

% Water in a Hydrate

To find the percent of water in

a hydrate, use the same

formula, except:

% Water = x 100Mass water

Mass compound

For Example:

What is the percent water in

CuSO4•5H2O?

For Example:

What is the percent water in

CuSO4•5H2O?

% Water = 90.074 g water x 100 = 36.1 % water

249.676 g compound

Try this:

What is the percent water in

BaCl2 • 3H2O?

Try this:

What is the percent water in

BaCl2 • 3H2O?

% Water = 54.0444 g water x 100 = 20.6 % water

262.2774 g compound