Cliffs AP Chemistry, 3rd Edition

Experiment 1: Determination of the Empirical Formula of a Compound

Background:Many elements combine with oxygen or other nonmetals in various ratios; i.e.
FeO, Fe 2 O 3 , Fe 3 O 4. This phenomenon demonstrates the Law of Multiple Proportions. In this ex-
periment, you will analyze the ratios in which lead and chlorine can combine and from the data
provided, be able to determine the empirical formulas of the compounds produced.

Scenario:A student was given 2.982 grams of a sample of a pure anhydrous lead chloride,
Compound A. The student added a small amount of water to the test tube and heated it in a
fume hood liberating chlorine gas and creating Compound B. A flask filled with 0.5 M NaOH
and gently swirled helped to trap the chlorine gas (see Figure 1).

Figure 1

The student then heated Compound B, driving off the remaining water, and determined the
mass of Compound B as 2.364 g. The student then reduced Compound B with hydrogen gas to
form elemental lead (see Figure 2). The chlorine in Compound B was driven off as HCl(g). This
lead was massed and found to weigh 1.770 g.

Rubber stopper

Large test tube and sample

Bunsen burner

0.5 M NaOH

500 ml

Florence flask

Glass tubing

Laboratory Experiments