Math of Chemical Formulas Review Key
Please answer on a separate sheet of paper
1. What is the difference between empirical formula and molecular formula?
Empirical Formula: Simplest form of the formula
Molecular Formula: Depends on how much the molecular mass is and is not the simplest
form.
2. 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.
Empirical Formula: NaClO4
Molecular Formula: NaClO4
3. 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.
*Use 92 g/mol as the molar mass*
Empirical Formula:NO2
Molecular Formula: N2O4
4. Naphthalene is a carbon and hydrogen containing compound often used in moth balls. The
empirical formula is C5H4 and its molar mass is 128.16g/mol. Find the molecular formula.
Molecular Formula: C10H8
5. A compound with the following composition has a molar mass of 60.10g/mol: 39.97% carbon;
13.41% hydrogen; 46.62% nitrogen. Find the molecular formula.
Molecular Formula: C2H8N2
6. How is a hydrate different from other chemical compounds?
The water is wrote separately from the salt when writing the formulas.
7. A hydrate of magnesium sulfate has a mass of 13.52 g. This sample is heated until no water
remains. The MgSO4 anhydrate has a mass of 6.60 g. Find the formula of the hydrate.
MgSO4 × 7 H2O
8. A sample of copper (II) sulfate hydrate has a mass of 3.97 g. After heating, the CuSO4 that
remains has a mass of 2.54 g. Determine the correct formula of the hydrate.
CuSO4 × 5 H2O
9. When 5.00 g of FeCl3 · xH2O are heated, 2.00 g of H2O are driven off. Find the chemical
formula and the name of the hydrate.
FeCl3 × 6 H2O
10. How many moles of tin (II) fluoride are there in 908 grams of tin (II) fluoride?
Tin (II) fluoride = SnF2
5.80 moles of Tin (II) fluoride
11. What would be the mass, in grams, of 1.505 x 1023 molecules of carbon disulfide?
Carbon disulfide = CS2
19.03 g of carbon disulfide
12. What volume, expressed in liters, would 50.0 grams of fluorine occupy?
59.0 L of Fluorine
13. How many molecules are there in 995 liters of sulfur dioxide?
2.67 × 1025 molecules of sulfur dioxide