10.3. Chemical Formulas http://www.ck12.org
FIGURE 10.15
Acetic acid (left) has a molecular formula
of C 2 H 4 O 2 , while glucose (right) has a
molecular formula of C 6 H 12 O 6. Both have
the empirical formula CH 2 O.Sample Problem 10.15: Determining the Molecular Formula of a Compound
The empirical formula of a compound that contains boron and hydrogen is BH 3. Its molar mass is 27.7 g/mol.
Determine the molecular formula of the compound.
Step 1: List the known quantities and plan the problem.
Known
- empirical formula = BH 3
- molar mass = 27.7 g/mol
Unknown
- molecular formula =?
Step 2: Calculate.
- The empirical formula mass (EFM) = 13.84 g/mol
molar mass
EFM
=
27. 7
13. 84
= 2
3. BH 3 ×2 = B 2 H 6
The molecular formula of the compound is B 2 H 6.
Step 3: Think about your result.
The molar mass of the molecular formula matches the molar mass of the compound.