What is percent composition?
Everything is made up of other things.
Pizza is a compound made form different things
Percent composition quantifies the components and
transforms them as a percentage of the whole
Empirical formula- formula of a chemical compound is the
simplest whole number ratio of atoms of each element present
in a compound
Glucose = CH2O
Molecular formula- formula that identifies each constituent
element by its chemical symbol and indicates the number of
atoms of each element found in each discrete molecule of that
Glucose = C6H12O6
Empirical formula exercise
Example Problem: A compound was analyzed and found to contain 13.5g Ca,
10.8g O, and 0.675g H. What is the empirical formula of the compound?
Start with the number of grams of each element, given in the problem.
Ca = 13.5g, O = 10.8g, H = 0.675g
Convert the mass of each element to moles using the molar mass from the periodic table.
Divide each mole value by the smallest number of moles calculated. Round to the nearest
whole number. This is the mole ratio of the elements and is represented by subscripts in the
Percent Composition Formula
To calculate the percent composition of
a component in a compound:
1.Find the molar mass of the compound by
adding up the masses of each atom
in the compound using the periodic table
2.Calculate the mass due to the component
in the compound you are solving by
adding up the mass of these atoms.
Divide the mass due to the component
by the total molar mass of the compound
and multiply by 100.
Calculate the percent by weight of sodium (Na) and chlorine (Cl) in sodium chloride (NaCl)
Na + Cl NaCl
Calculate the molecular mass (MM):
MM = 22.99 (Na) + 35.45(Cl) = 58.44
Calculate the total mass of Na present:
1 Na is present in the formula, mass = 22.99
Calculate the percent by weight of Na in NaCl:
%Na = (mass Na ÷ MM) x 100 = (22.99 ÷ 58.44) x 100 = 39.34%
Calculate the total mass of Cl present:
1 Cl is present in the formula, mass = 35.45
Calculate the percent by weight of Cl in NaCl:
%Cl = (mass Cl ÷ MM) x 100 = (35.45 ÷ 58.44) x 100 = 60.66%
The answers above are correct if %Na + %Cl = 100, that is,
39.34 + 60.66 = 100.
Think of a sea turtle egg as a mixture or a
Egg = shell x grams +yolk x grams + albumen x grams + water x grams
Loggerhead sea turtles lay multiple clutches over the
Each clutch has 30-40 eggs
The mother sea turtle provides no post hatching care
Yolk – provides energy and building material
Albumen – provides antibodies
Water – used in embryogenesis
Shell – protects the developing embryo
Wet component analysis
How much investment (nutrients)
are in the eggs?
We quantify investment by
weighing egg components:
egg mass and albumen level
decreases throughout the
yolk level does not change across
the nesting season
Dry component analysis
Dry component analysis- takes out the water and
leaves only nutrients.
Yolk – does not change throughout nesting season
Albumen – does not change throughout nesting season
So what is changing throughout the
Ash Free Dry Mass
Study used to separate organic materials from
Yolks are theoretically 56% organic
Therefore 56% of the yolk is used for energy
what is the other 44% used for?
made up of ?
Everything is made up of other things!
Everything you see is a molecule or is build up of
Humans are comprised of: Oxygen 65% Carbon
18% Hydrogen 10% Nitrogen 3% Calcium 1.5 %,
Trace Elements 2.5%.
So an average 70 kg adult is 43g of Oxygen, 16g
of Carbon, 7grams of Hydrogen, 1.8 of Nitrogen
and 1.0 gram of Calcium, and 1.2 grams of Trace
DNA is a component too
Think of DNA as a compound made up of many
A sugar backbone, nucleotide bases, and phosphate
Each piece is used to make a DNA strand however,
DNA can be comprised of more of one component
than the other.
% composition of trail mix –
comparing data and graphing contents as
a pie chart.
Candy DNA Models – to test if
candy models are compositionally