What Goes Around, Comes Around
A Cycle of Copper Reactions
Objectives: 1) To determine if chemical reactions or physical changes occurred during
a series of reactions involving copper and its compounds. 2) To attempt to verify the Law
of Conservation of Matter.
Background Information: Write a paragraph or so explaining the following topics:
1) chemical reactions and equations, 2) types of chemical reactions, and 3) the Law of
Conservation of Matter.
Chemistry; Write balanced chemical equations in standard form for the five reactions
you will carry out in the lab. They are described below. Include state symbols.
Reaction 1: A sample of solid copper will be mixed with nitric acid to produce
aqueous copper (II) nitrate, nitrogen dioxide gas, and water. This is called a redox
reaction.
Reaction 2: Aqueous copper (II) nitrate reacts with aqueous sodium hydroxide in
a double replacement reaction to produce solid copper (II) hydroxide and aqueous
sodium nitrate.
Reaction 3: The copper compound produced in reaction 2 decomposes by heating
to produce solid copper (II) oxide and water.
Reaction 4: The copper compound produced in reaction 3 reacts with sulfuric acid
in a double replacement reaction to form aqueous copper (II) sulfate and liquid
water.
Reaction 5: The copper compound in reaction 4 reacts with solid zinc in a single
replacement reaction to produce solid copper and aqueous zinc (II) sulfate.
Materials: List the materials you will use for this lab, and if appropriate, the sizes of
equipment and amounts of substances. (Hints: 1) read the lab procedure 2) graduated
cylinder come in sizes of 10 ml, 25ml, and 50 ml, and may be washed and reused during
an experiment.)
Procedure:
1. *Obtain a sample of copper from the instructor. Make sure you record the
number of your sample.
2. Start a hot water bath for later in the procedure by placing about 250mL of
deionized water in a 400 mL beaker and put the beaker on the hot plate. Turn the
hot plate onto medium-to-high heat. If it boils before you need the water, turn it
down to low.
3. *Caution: If you have asthma (even an extremely mild case), you are not to
do this step, nor are you allowed to be around the fume hood during this
step. Label a 250 mL beaker with your names (use masking tape and a Sharpie.)
Place your sample of copper in the beaker. Take the beaker to the fume hood.
TEACHER MUST BE PRESENT AT THE FUME HOOD!!!! The teacher
will measure about 4 mL of nitric acid into a 10 mL graduated cylinder (Wear
gloves!) and add it to the beaker with the copper in it. Close the window of the
fume hood, and wait until the copper has reacted and the gas has dissipated.
Reaction 1 has just occurred!
4. Take the beaker back to your desk. Add deionized water (not the stuff you are
heating) until the beaker is about half full.
5. *While stirring this solution with a glass stirring rod, add about 30 mL of sodium
hydroxide solution. This is Reaction 2! Wash the graduated cylinder and rinse it
with deionized water so it may be used again later.
6. *With constant stirring, heat the solution to nearly boiling. Use a small amount of
water from your wash bottle to get as much of the solid off the stirring rod. Use a
Bunsen burner for the heating process. Remove the beaker from the heat (hot
hands!), and continue stirring for a minute or so to ensure complete reaction.
Allow the solid to settle. Reaction 3 is now complete!
7. Decant (carefully pour the liquid from the beaker, while keeping all of the solid in
the beaker) the solution into the sink – the more solid you lose down the sink, the
worse your results will be.
8. *Using hot hands, add about 200mL of your hot deionized water to the solid in
the beaker, swirl, allow the solid to settle, and decant again. This step washes
the copper compound of contaminants. Turn the hot plate down to low.
9. *Add, with stirring, about 15 mL of sulfuric acid to the solid in the beaker. This is
Reaction 4! Wash the graduated cylinder and rinse it with deionized water so it
may be used again later.
10. *“Weigh out” about 2 grams of granulated zinc.
11. *In the fume hood, add, all at once, the 2 grams of zinc to the beaker. Reaction 5
is now occurring! Stir/swirl until the production of gas ceases.
12. *If the solution is still bluish (indicating unreacted copper ions), add a small
amount of granulated zinc. If you see unreacted zinc in the bottom of the beaker,
add (in the fume hood) about 10 mL of hydrochloric acid to the beaker and warm
it on a hot plate. Wait for any bubbling to cease. Wash the graduated cylinder and
rinse it with deionized water so it may be used again later.
13. *Decant the liquid into the sink. Wash the solid with about 5 mL of methanol and
decant. Wash the graduated cylinder and rinse it with deionized water so it may
be used again later.
14. Use a balance and determine the mass of a clean evaporating dish.
15. *Transfer the solid into the evaporating dish. Be sure to get all of the solid into
the evaporating dish. You may use a small amount of deionized water from your
wash bottle to help rinse out the solid from the beaker. Use as little water as
possible, as you will have to evaporate all the water in the next step.
16. *Place the evaporating dish with a watch glass on top (in the convex position) on
a hot plate that is on low heat. Heat until all the water is evaporated. If the solid
begins to darken, stop!!!! This means another reaction is taking place, and you are
turning the copper into another compound. Removing the watch glass from the
evaporating dish, making sure you use tongs, as it will be hot.
17. Determine the mass of the copper and the evaporating dish.
18. Clean up. Be sure to put the copper in the designated container.
19. Ask your instructor for the actual amount of copper you started with.
Data: Prepare blank data tables as shown below for this experiment. As you perform the
experiment, fill out the tables.
Copper Lab Measurements
Mass of empty evaporating dish(g) (step 14)
Mass of evaporating dish and copper (g) (step 17)
Mass of copper from instructor (g) ( step 19)
Observations for Copper Lab
Step Number
1
Observations*
3
5
6
8
9
10
11
12
13
15
16
*Observations should be made before, during, and after each step as appropriate.
Calculations/Analysis:
1. Calculate the mass of copper recovered. ( Mass of evaporating dish and copper –
mass of evaporating dish)
2. Calculate the % recovery using the equation
% recovery = [mass recovered / initial mass*] x 100
*initial mass is mass given to you by teacher in step 19
Results:
1. Report the amount of copper you ended up with and your percent recovery in a
complete sentence. Don’t forget your sample number!
2. For each starred step in the procedure, determine if a physical change &/or a
chemical reaction occurred. Give a specific reason for your determination (a new
substance was or was not formed is not a specific reason.) You can make a table
for this if you would like.
Conclusion/Discussion:
Write a conclusion in paragraph format, that includes the answers to the following.
1. Were you successful in achieving the objectives of this lab? (Think about –
Could you determine if a chemical reaction occurred? Could you determine if a
physical change occurred? Did you prove the Law of Conservation of Matter?)
Why?
2. From your observations, what color are most solutions containing copper ions?
Would this piece of information be useful in a qualitative analysis experiment?
Why?
3. Why didn’t the product of this lab look exactly like the starting material?
4. What errors occurred in this experiment? How would these errors affect the
results of your experiment? How could you reduce these errors or limit their
effect?