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