SCH 3U
Experiment: Percent Yield
Names:
Purpose: To determine the percentage yield in a reaction between copper (II) chloride and aluminum.
Materials
CuCl2 • 2H2O (copper (II) chloride dihydrate)
10 cm x 10 cm piece of aluminum foil
hot plate
tongs
watch glass
2 - 250 mL beakers
water
stirring rod
tweezers
scale
Procedure
1. Mass a clean, dry 250 mL beaker.
2. Add 1.50 g of copper (II) chloride dihydrate and 50 mL water.
3. Stir the mixture with a glass stirring rod until all the compound has dissolved.
4. Mass a 10 cm by 10 cm piece of aluminum foil.
5. Fold the piece of aluminum foil lengthwise to form a 5 cm by 10 cm strip. Fold this strip lengthwise
again to make a 2.5 cm by 10 cm strip. Loosely coil this strip around a pencil and put the aluminum
coil into the solution. You may gently immerse it into the solution with the stirring rod.
6. Place the beaker on a hot plate and heat the solution with a hot plate until it has boiled GENTLY for
5 minutes. Avoid overheating. Allow the solution to cool until you can touch the beaker with your
hand.
7
Carefully remove any aluminum foil from the beaker with tweezers. Leave all the copper metal in
the beaker. Decant (pour off) the liquid part into a separate beaker. Add approximately 50 mL of
water to the copper and rinse by decanting the liquid off again.
8. Cover the beaker partially with a watch glass and then gently heat the beaker with the wet copper
until all the water has evaporated. When the spattering has stopped, remove the watch glass and
continue gentle heating until only the copper remains. Be careful not to overheat and turn the copper
black.
9. Allow the beaker to cool and determine the mass of the beaker and the copper.
Quantitative Observations
4.
1.
mass of aluminum foil =
2.
mass of empty beaker =
3.
mass beaker plus copper (II) chloride dihydrate =
mass beaker plus copper
=
Qualitative Observations
Before
During
After
Questions and Calculations (Show all of your work for any calculations)
1. mass of copper (II) chloride dihydrate =
2. mass of copper =
3. a) According to your qualitative observations, which reactant was present in excess?
b) According to your qualitative observations, which reactant was the limiting reactant?
c) Do stoichiometric calculations to support your observations of the limiting reactant.
CuCl2 · 2 H2O +
4.
Al →
Cu +
AlCl3 +
H2O
What is the theoretical yield of copper when 1.50 g of copper (II) chloride dihydrate reacts with
excess aluminum according to the following unbalanced chemical equation?
CuCl2 · 2 H2O +
Al →
Cu +
AlCl3 +
H2O
5. a) Calculate the percentage yield of copper.
b) Why wasn’t it 100% yield? Discuss at least three sources of experimental error.
Conclusion (one sentence please.)
Discussion Questions (Show all of your work for any calculations)
1. What mass of aluminum would be required to react with 1.50 g of copper chloride dihydrate?
2. What mass of aluminum chloride would be formed if 3.00 g of aluminum were reacted with 3.00 g
of copper (II) chloride dihydrate?
3. Magnesium and hydrogen chloride react according to the following skeleton equation;
Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)
a) Balance the skeleton equation.
b) Examine the equation carefully. What evidence would you have that a reaction was taking place
between the hydrochloric acid and the magnesium?