Mass Relationship in a Chemical Reaction

Name:
Mass Relationship in a Chemical Reaction
Purpose: To determine the mass of copper produced and the % yield of copper
when copper (II) chloride dihydrate is reacted with aluminum metal.
Materials: Copper (II) chloride dihydrate (CuCl2 ● 2H2O ) and aluminum foil,
beaker, stir stick, Bunsen burner, watch glass, lighter, tweezers, scale
Method:
1. Determine the mass of a clean, dry 150 mL beaker. Add exactly 2 grams of
copper (II) chloride dihydrate to the beaker.
2. Add 50 mL of water to the beaker and stir with a glass rod until the crystals have
dissolved. (Note the colour of the solution.)
3. Fold a piece of 6 cm x 10 cm aluminum foil into a strip and bend it into a circle
and put it into the solution in the beaker.
4. Heat the solution and let it boil gently for 5 minutes. There may be foaming in the
first minutes. Don’t heat too strongly. Let the solution cool. (Note the colour of the
solution and the solid product.)
5. Using tweezers, carefully remove as much aluminum foil as possible. Try not to
take too much copper with it.
6. Decant the liquid into the drain as demonstrated by the teacher. Add 30 mL of
water to the beaker. Stir well with the glass rod and decant the water into the
drain. Repeat with another 30 mL of water.
7. Heat the beaker gently to dry the product. If the product starts to turn black, you
are heating too strongly.
8. Let the beaker cool and mass the beaker and its contents. Record the mass.
Data Table:
Mass of empty Beaker
Mass of beaker and CuCl2 ● 2H2O
Exact mass of CuCl2 ● 2H2O added
Mass of beaker and copper after heating
Mass of just the copper
I ) What two observations indicate that your reaction is complete?
________________________________________________________________________
II) Based on what you visually see, what reactant is in excess (left over)? ____________
Calculations:
1. Below is the reaction that you carried out. If you removed the H2O portions of
the reaction, what type of reaction did you carry out?
_____________________________________________
3CuCl2 ● 2H2O + 2Al  3Cu + 2AlCl3 + 6H2O
2. i)What is the mole ratio of copper (II) chloride dihydrate to Copper? _______
ii) What is the mole ratio of copper (II) chloride dihydrate to aluminum? _______
3. Determine the molar mass of CuCl2 ● 2H2O _________________
This dot means add 2 water molecules onto this compound as it is a hydrated
compound
4. Using the 4 step mass-mass calculation taught in class, determine how many
grams of copper you should have made when 2 g of copper (II) chloride
dihydrate reacts with excess aluminum.
3CuCl2 ● 2H2O + 2Al  3Cu + 2AlCl3 + 6H2O
5. Looking at your actual yield of copper obtained from the lab, calculate your
percent yield.
6. List 2 specific reasons as to why your percent yield is not 100%.
7. How many grams of aluminum would be required to react with 2.0 g of copper
(II) chloride dihydrate? [ mass –mass problem]
8. How would the results of the experiment been affected if you had not used an
excess of aluminum?
9. How would the results have been affected if you had heated the copper so
strongly that it turned black?
10. Would a chemical reaction take place if a piece of copper was placed in a
solution of Aluminum sulphate? Explain [hint: look at activity series]