AS Chemistry
U2 HW4: Empirical & Molecular Formulae
Name: ________________________________________________________
Due Date: __________
Find the empirical formula
Use the following sets of data to calculate the empirical formula of each of these compounds.
1. Octane is a hydrocarbon. 5.00 g of octane contains 4.21 g of carbon.
2. 6.45 g of aluminum sulfide contains 2.32 g of aluminum.
3. Orthoclase, a mineral in feldspar, is a compound of potassium, aluminum, silicon
and oxygen. 20.00 g of orthoclase contains 2.81 g of potassium, 1.94 g of aluminum
and 6.04 g of silicon.
Phosphorus and sulfur form several different compounds. The following sets of data give the mass of phosphorus
contained in 1.000 g of each of these three compounds. Calculate the empirical formula of each compound.
4. In 1.000 g of compound A contains 0.356 g of phosphorus.
5. In 1.000 g of compound B contains 0.564 g of phosphorus.
6. In 1.000 g of compound C contains 0.437 g of phosphorus.
U2: Atoms, Molecules & Stoichiometry
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AS Chemistry
U2 HW4: Empirical & Molecular Formulae
Find the molecular formula.
7. What’s the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0%
oxygen?
8. If the molar mass of the compound in problem 7 is 73.8 grams/mole, what’s the molecular formula?
9. Find the molecular formula of a compound with an empirical formula of C4H4O and a molar mass of
136 grams per mole.
10. Find the molecular formula of a compound with an empirical formula of C2H8N and a molar mass of 46
grams per mole.
11. A component of protein called serine has an approximate molar mass of 100 g/mole. If the percent
composition is as follows, what is the empirical and molecular formula of serine?
C = 34.95 % H= 6.844 % O = 46.56 % N= 13.59 %
U2: Atoms, Molecules & Stoichiometry
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