Empirical and Molecular Formula Practice
1. A compound contains 18.8% sodium, 29.0% chlorine, and 52.2% oxygen, by mass. If the molar mass
of the compound is 122.44 g/mol, determine the empirical and molecular formulas.
2. A 4.99 gram sample of a compound contains 1.52 grams of nitrogen atoms and 3.47 grams of oxygen
atoms. The molar mass of the compound is between 90.0 g and 95.0 g. Determine the empirical and
molecular formulas. Also, calculate the actual molar mass of this compound.
3. Ascorbic acid is another name for Vitamin C. It is composed of 40.92% carbon, 4.58% hydrogen, and
54.50% oxygen, by mass. Determine the empirical formula for ascorbic acid.
4. H3PO4, Phosphoric acid, is used in detergents, fertilizers, toothpastes and flavoring in carbonated
beverages. Calculate the percent composition by mass to two decimal places of H, P and O in this
compound.
5. What is the percent composition by mass of aspartame (C14H18N2O5), the artificial sweetener
NutraSweet?
6. Ascorbic acid (vitamin C) is 40.92% C, 4.58% H and 54.50% O by mass. What is the empirical
formula of ascorbic acid?
7. What is the empirical formula of each of the following compounds?
a. Talc by mass composition contains 19.2% Mg, 29.6% Si, 42.2% O and 9.0% H.
b. Saccharin has by mass composition 45.89% C, 2.75% H, 7.65% N, 26.20% O and 17.50% S
c. Salicylic Acid, used in aspirin, contains 60.87% C, 4.38% H, and 34.75% O by mass
composition.
d. L-Dopa, a drug used for the treatment of Parkinson’s disease, is 54.82% C, 5.62% H, 7.10% N,
and 32.46% O by mass composition.
8. What is the molecular formula of benzoyl peroxide (the empirical formula is C7H5O2) if the
molecular mass is 242 g/mol?
Hydrate Practice Problems
1. Calculate the percent water in each of the following hydrates:
a) Strontium chloride hexahydrate
b) Zinc sulfate heptahydrate
c) Beryllium nitrate trihydrate
2. Calculate the percentage of the given element in each of the following
hydrates:
a) Nickel in nickel (II) acetate tetrahydrate
b) Chromium in sodium chromate tetrahydrate
c) Cerium in cerium (IV) sulfate tetrahydrate
3. Heating copper (II) sulfate pentahydrate will evaporate the water from the
crystals, leaving anhydrous copper (II) sulfate. What mass of anhydrous
copper (II) sulfate would be produced by heating 500.0 grams of copper
(II) sulfate pentahydrate?
4. Magnesium sulfate heptahydrate is heated until all the water is driven off.
The sample loses 11.80 grams upon heating. What was the mass of the
original sample?
5. A 5.018 gram sample of a certain hydrate of magnesium sulfate,
MgSO4•xH2O, is heated until all the water is driven off. The resulting
anhydrous compound weighs 2.449 grams. What is the formula of the
hydrate?
6. Anhydrous sodium sulfate can absorb water vapor and be converted to
the decahydrate. By how many grams would the mass of a 1.00 gram
sample of the anhydrous compound increase if exposed to enough water
to produce the decahydrate?
7. A certain hydrate is found to have the following percent composition by
mass: 20.3% Cu, 8.95% Si, 36.3% F and 34.5% H2O. What is the formula of
this hydrate?
8. A 4.175 gram sample of a certain hydrate of copper (II) sulfate,
CuSO4•xH2O, is heated until all the water is driven off. The resulting
anhydrous compound weigh 3.120 grams. What is the formula of the
hydrate?