SCH3U Fall 2012 Unit 3 - Stoichiometry
SCH3U
Name: ________________
Mass Relationships in a Chemical Reaction
Purpose
To determine the mass of copper formed when Aluminum reacts with a copper salt.
Introduction
In this experiment, a piece of aluminum foil will be placed in an aqueous solution of Copper II chloride. The
reaction may or may not go to completion. The mass of copper produced when a given mass of the copper
compound reacts with a given aluminum will be determined experimentally. This will be compared to a
theoretical yield calculated from an analysis (based on a balanced equation) of which reactant is limiting and the
expected mass of product.
Apparatus
2 150 mL beakers
graduated cylinder
stirring rod
tweezers
Materials
CuCl2•2H2O
Aluminum foil
watch glass
balance
hot plate
Procedure
Record all experimental results in the data table as soon as you obtain them.
a) Mass of first beaker (g)
b) Mass of beaker and anhydrous Copper II chloride (g)
c) Mass of dry Copper II chloride dihydrate (g)
d) Mass of Aluminum foil (g)
e) Mass of beaker and Copper (g)
f) Mass of Copper (g)
g) Mass of unreacted Al (s) if applicable
h) Appearance of Copper II Chloride solution
i) Appearance of Aluminum
j) Appearance of the contents of the beaker after reaction
A) Determine the mass of a clean, dry 150 mL beaker.
To the beaker add approximately 2.5 g of anhydrous copper II chloride. Determine the mass of the beaker and
contents. Add 50 mL of water. Stir to dissolve the copper compound.
B) Group 1: Weigh out about 0.50 g of aluminum foil and tear small strips into the beaker with the copper
solution.
Group 2: Weigh out about 0.25 g of aluminum foil and tear small strips into the beaker with the copper solution.
C) There may be some foaming during the early stages of the reaction and heat will be produced. Gently stir the
foil with a stirring rod to cause copper to fall off and expose more aluminum. Continue to stir occasionally until
all signs of a reaction have stopped.
D) Carefully use tweezers to shake any remaining aluminum foil in the beaker to dislodge the copper. Remove
the aluminum foil, being careful to leave the copper in the beaker. Rinse and dry this aluminum using filter
paper and subtract its mass from the mass of aluminum in the data table.
E) Pour the liquid in the beaker into the other beaker, being careful not to lose any copper. When you are sure
that no copper has been lost, you may pour the contents of the second beaker into the sink.
F) Add 50 mL of water to the beaker. Stir gently to wash the copper and repeat step E. Repeat step F
H) If time allows, heat the cooper to drive off the water and weigh once cooled down. If there is not time, leave
the copper in the beaker to dry out over a few days and then weigh.
Concluding Questions
1) Write a balanced chemical equation for this reaction.
2) Calculate the molar mass of
Aluminum: ____________ Copper:___________________
Anhydrous Copper II chloride: ________________________________________________________
3) a) Determine the limiting reactant from the masses of the reactants and the balanced equation.
b) How does your answer to 3a compare to item “h” in the data table?
4) Calculate the theoretical yield of solid copper.
5) Calculate the percent yield.
6) Calculate the percent composition of CuCl2
6) What was the purpose of Step F? What would be the consequences of omitting this step?