Leftover Aluminum Wire
A Stoichiometry Lab
Background:
Stoichiometry is the branch of chemistry that deals with the numerical relationships and
mathematical proportions of reactants and products in chemical reactions. Chemical reactions are
represented by balanced chemical equations. Proper interpretation of an equation provides a great deal
of information about the reaction it represents and about the substances involved in the reaction.
In the experiment, aluminum wire will be added to an aqueous solution of copper(II)chloride
causing a single replacement oxidation-reduction reaction to take place. The oxidation of aluminum
metal to aluminum(III) will occur, which is apparent by the dissolving of the aluminum wire to form
aluminum chloride (AlCl3). The simultaneous reduction of copper(II) or copper(II) ions to copper metal
(Cu2+ to Cu0) will occur and solid copper metal will precipitate from solution. As the copper(II) ions are
reduced, the green-blue color will fade until the solution is completely colorless—the indication that the
reaction is complete.
Procedure:
1. Set up a hot water bath in a 400mL beaker using approximately 300ml of tap water. Bring the
water to a boil using a hot plate while performing steps 1-5.
2. Obtain approximately 0.50 g of copper(II)chloride crystals. Use a centigram balance to
determine the exact mass to the nearest hundredth of a gram. Record the mass in the data table.
3. Place the copper(II)chloride crystals in a 16x125mm test tube. Add 10ml of distilled water and
stir to dissolve the crystals.
4. Cut a 16- to 18-cm piece of aluminum wire with wire cutters. Use a small piece of steel wool to
shine the wire and to remove any surface impurities which may be present on the wire.
5. Measure and record the exact mass of the aluminum wire to the nearest hundredth of a gram in
the data table.
6. Use tweezers to lower the aluminum wire into the test tube containing the copper(II) chloride
solution. The wire will extend beyond the height of the tube. Place the test tube into the boiling
water bath for approximately 5-10minutes. The reaction is complete when the solution becomes
colorless.
7. Use tweezers to remove the wire from the test tube. Use caution so as not to disturb the copper
on the wire.
8. Measure the mass of a clean, dry evaporating dish and record the mass in the data table.
9. Use the spatula to scrape as much solid copper as possible from the aluminum wire into the
evaporating dish.
10. Allow the solid copper in the evaporating dish to dry overnight.
PROCEDURE CONTINUES ON BACK!!!!
11. Once dry, measure the mass of the copper and the evaporating dish. Record this mass in the data
table.
12. Rinse the aluminum wire with tap water to remove any impurities and dry the wire with a paper
towel. Once dry, measure and record the actual “Leftover” mass of the aluminum wire in the
data table.
13. Share data (not results) with your partner table for “trial 2”
Leftover Aluminum Wire Worksheet
Data Table
Trial 1
Trial 2
Trial 1
Trial 2
Initial mass of CuCl2∙2H2O (g)
Initial mass of aluminum wire (g)
Mass of “leftover” aluminum wire (g)
Actual mass of aluminum reacted (g)
Mass of evaporating dish + copper (g)
Mass of evaporating dish (g)
Actual mass of recovered dry copper (g)
Results Table
a. Moles of CuCl2∙2H2O
b. Moles of aluminum that should react
(theoretical)
c. Mass of aluminum that should react
(theoretical)
d. Percent error for reacted aluminum
e. Predicted mass of recovered copper
(theoretical)
f. Percent error for recovered copper
g. Percent yield of recovered copper
Post-Lab Questions and Calculations
1. Write the balanced chemical equation for the reaction that occurred between the aluminum wire and the
copper(II) chloride solution.
2. Which starting material in the reaction is the limiting reactant and which material is present in excess?
Show calculations and all your work for your determination of this.
3. Complete the Data Table and the Results Table. Show all calculations on a separate sheet of apper,
clearly indicating where each results came from for each box a through g.
4. What physical evidence do you have that shows that copper(II) chloride is, indeed, the limiting reactant?
5. Discuss reasonable and potential sources of error in this experiment.
6. Discuss potential reasons why the percent yield of recovered copper may be greater than 100%.
7. Why do you think that scientists add excess of one or more chemical when performing a reaction rather
than combine the exact stoichiometric ratio?
8. What factors do you think may lead scientists (in industry, for instance) to decide to use a certain starting
material as the limiting reactant and another as the excess chemical?