Empirical Formula – a
smallest whole number
ratio
Ionic compounds only
use an Empirical
Formula
Sugar
Salt
Molecular Formula – tells
exactly which and how
many atoms are attached
to each other in a molecule
of something
Molecular compounds can
use a Molecular
Formula and an
Empirical Formula
A chemical formula is a ratio of moles:
KBr means that for every mole of
potassium bromide, there is 1 mole of
K and 1 mole of Br
H2O means that for every mole of
water, there are 2 moles of H and 1
mole of O
If table salt was chemically analyzed and it was determined that a 58.44 g sample of
salt contains 22.99 g of Na and 35.45 g of Cl, what is the empirical formula of this
compound?
How many moles of
each element were
in the sample?
What is the ratio of Na
moles to Cl moles in
the sample?
What is the
empirical
formula for
this sample?
A mass spectrometer is a
device that can blast
compounds apart into
their pieces and collect
mass data for the
sample. Mass data can
be used to determine
empirical and molecular
formulas for unknown
compounds.
1. Turn mass data into moles of each element
2. Find the smallest whole number ratio
A mass spectrometer is used to analyze an ionic compound
containing only lithium and fluorine. A 38.9 g sample is determined to
have 28.49 g of fluorine and the rest lithium. What is the empirical
formula of this compound?
Why must you find a
WHOLE NUMBER
ratio?
Percent
Use 100g
Mass
Use molar mass
Moles
Divide all by
smallest number;
multiply all by
whole numbers
as needed
Molecular
Formula
Use molar mass
of compound
Empirical
Formula
Smallest whole
number ratio
(Percent)MassMolesSmallest-whole-number-ratio
(divide all by smallest number, multiply all by whole numbers as
needed)Empirical formula(Molecular formula)
A compound containing only sulfur and oxygen is
decomposed and analyzed for mass data. The
entire compound had a mass of 1.440954 g and
0.48099 g of sulfur was isolated from the compound.
Find the empirical formula for this compound.
(Percent)MassMolesSmallest-whole-number-ratio
(divide all by smallest number, multiply all by whole numbers as
needed)Empirical formula(Molecular formula)
A compound is decomposed and analyzed for
mass data. The compound is composed of 7.2066
g C and 1.51185 g H. In a separate experiment, the
compound is found to have a molar mass of 87.2
g/mol. Find the empirical and molecular formulas
for this compound.
(Percent)MassMolesSmallest-whole-number-ratio
(divide all by smallest number, multiply all by whole numbers as
needed)Empirical formula(Molecular formula)
A compound is analyzed for composition and found to
be 23.76% S, 52.53% Cl, and the rest oxygen. What is
the empirical formula for this compound?
A compound is analyzed for composition and found to be 23.76% S,
52.53% Cl, and the rest oxygen. What is the empirical formula for this
compound?
(Percent)MassMolesSmallest-whole-number-ratio
(divide all by smallest number, multiply all by whole numbers as
needed)Empirical formula(Molecular formula)
A hydrated compound, FeSO4.xH2O, was heated
carefully to remove the water without decomposing
the compound. The initial compound had a mass of
16.46 g. After the water was removed the
compound had a mass of 12.14 g. Find the
empirical formula for the hydrated compound.