Empirical and Molecular Formula Extra Practice
Empirical Formula Calculations:
A. An unknown compound is found to be 52.94% aluminum and 47.06% oxygen. What is the
empirical formula?
B. An unknown compound is found to be 82.25% nitrogen and 17.75% hydrogen. What is the
empirical formula?
C. Baking soda is found to be 57.13% oxygen, 27.38% sodium, 14.29% carbon, and 1.20%
hydrogen. What is the empirical formula?
D. An unknown gas is found to be 57.12% oxygen and 42.88% carbon. What is the empirical
formula?
E. An unknown compound is found to be 92.20% chlorine and 7.80% carbon. What is the
empirical formula?
F. An amethyst geode is found to be 46.76% silicon and 53.24% oxygen. What is the empirical
formula?
G. An unknown toxic compound is found to be 75.73% arsenic and 24.27% oxygen. What is the
empirical formula?
H. An unknown solid found near a volcano is found to be 49.92% oxygen and 50.08% sulfur.
What is the empirical formula?
I. An unknown gas is found to be 27.93% phosphorus and 72.07% oxygen. What is the empirical
formula?
J. An extremely poisonous gas is found to be 51.84% nitrogen, 44.44% carbon and 3.73%
hydrogen. What is the empirical formula?
K. Laughing Gas is found to be 63.65% nitrogen and 36.35% oxygen. What is the empirical
formula?
L. A toxic compound is found to be 71.17% selenium and 28.83% oxygen. What is the empirical
formula?
M. An unknown gas is made up of 2.67 grams of carbon and 7.11 grams of oxygen. What is the
empirical formula?
N. An unknown compound is made up of 3.2 grams of oxygen and 2.8 grams of nitrogen. What is
the empirical formula?
O. An unknown compound is found to have 5.3 grams of oxygen and 3.6 grams of sulfur. What is
the empirical formula?
P. A sample of silver ore is found to have 14.5 grams of silver and 2.2 grams of sulfur. What is
the empirical formula?
Q. A sample of tin ore is found to have 9.13 grams of tin and 2.46 grams of oxygen. What is the
empirical formula?
R. A sample of copper ore is found to have 41.9 grams of copper and 10.7 grams of sulfur. What
is the empirical formula?
S. A sample of pyrite is found to have 18.6 grams of iron and 21.4 grams of sulfur. What is the
empirical formula?
Empirical and Molecular Formula Calculations:
T. A Sample of a gas was found to be 30.45% nitrogen and 69.55% oxygen. That is the
empirical formula? The molar mass of the gas was found to be 92.02 g/mol. What is the
molecular formula?
U. A molecular solid compound was analyzed and found to contain 32.63% phosphorus and
67.37% oxygen. What is the empirical formula? Later, the molar mass of the solid was
found to be 190 g/mol. What is the molecular formula?
Summary:
You will always need to find the empirical formula to be able to find the molecular formula.
Find the empirical formula first and then use the molar mass to calculate the ratio of the
empirical formula to the molecular formula and multiply by the factor. Don’t forget that you
are starting with experimental data so rounding to whole numbers should be a part of your
work.
Molecular Formula Calculations—don’t forget that you need the
empirical formula to find the molecular formula:
AA.
An unknown acid is found to have 39.99% carbon, 53.30 % oxygen and 6.72% hydrogen.
The molecular weight of the compound is 60.04 g/mol. What is the molecular formula?
BB.
A component of antifreeze is found to be 51.56% oxygen, 38.70% carbon, and 9.74%
hydrogen. The molecular weight is 62.1 g/mol. What is the molecular formula?
CC.
An unknown organic compound is found to be 92.26% carbon and 7.74% hydrogen. The
molecular weight is 26.018 g/mol. What is the molecular formula?
DD.
An unknown solvent has 6.0 grams carbon, 8.0 grams oxygen and 1.5 grams of hydrogen.
The molecular weight is 124.1 g/mol. What is the molecular formula?
EE.
An unknown solvent is composed of 51.44 grams of carbon and 4.32 grams of hydrogen.
The molecular weight is 78.07 g/mol. What is the molecular formula?
FF.
An unknown solvent is found to be 64.81% carbon, 13.60% hydrogen and 21.59% oxygen.
The molecular weight is 74.12 g/mol. What is the molecular formula?
GG.
An unknown solvent is found to be 3.9 of grams phosphorus and 22.2 grams of chloride.
The molecular weight is 208.5 g/mol. What is the molecular formula?
HH.
An unknown sample is composed of 20.19% phosphorus, 10.43% oxygen and 69.38%
chlorine. The molecular weight is 153.5 g/mol. What is the molecular formula?
II.
An unknown sample is composed of 8.0 grams of carbon, 10.7 grams of oxygen and 1.3
grams hydrogen. The molecular weight is 180.2 g/mol. What is the molecular formula?
JJ.
An unknown compound is composed of 91.92% bromine and 8.08% silicon. The molecular
weight is 347.7 g/mol. What is the molecular formula?
KK.
An unknown hydrocarbon is found to be 82.69% carbon and 17.31% hydrogen. The
molecular formula is 58.1 g/mol. What is the molecular formula?
LL.
An unknown sample of rubber is found to be composed of 9.1 grams of carbon and 1.5
grams of hydrogen. The molecular weight is 56.1 g/mol. What is the molecular formula?
MM. An unknown compound is found to be 33.30% nitrogen, 57.11% carbon, 9.59% hydrogen.
The molecular weight is 84.1 g/mol. What is the molecular formula?
NN. An unknown compound is found to be composed of 15.0 grams of carbon and 1.3 grams of
hydrogen. The molecular weight is 78.1 g/mol. What is the molecular formula?
OO. A sample of an unknown substance is found to contain 12.9 grams of nitrogen and 37.0
grams of oxygen. The molecular weight is 216 g/mol. What is the molecular formula?
PP.
An unknown compound is found to be composed of 92.3% carbon and 7.7% hydrogen. The
molecular weight of the compound is 104.2 grams. What is the molecular formula?
QQ. A sample of caffeine is found to be composed of 49.47% carbon, 5.19% hydrogen, 28.86%
nitrogen and 16.48% oxygen. The molecular weight is 194.2 g/mol. What is the molecular
formula?