Chemistry Teaching Center
Stony Brook University
Copper Cycle Lab
Advanced Study Questions:
1. The net ionic equations are shown on the lab procedure. Based on the information from
the procedure, write the balanced molecular equations for each step and prove that the
net ionic equations are valid.
2. Examine the above reactions and identify them as precipitation, metathesis, acid-base
neutralization, redox, combination, decomposition, displacement, or combustion. If a
reaction falls into more than one category, list all possibilities.
3. In the second reaction, a side reaction is also occurring. Write the balanced molecular
and net ionic equation for this process. Identify the reaction type(s).
4. An additional 0.2 grams of aluminum is added to the reaction. Explain the purpose of
adding the additional aluminum.
5. Hydrochloric acid is added in the last step. Explain the purpose of adding the acid in this
step. If any additional reactions occur in this step, write a balanced net ionic equation
for this side reaction.
6. 1.25 grams of copper was added in the first step. After filtration, 1.12 grams of copper
was recycled after step 5. Calculate the percent yield for this experiment.
Conclusion Questions:
Q1. In the copper cycle experiment, you added sequentially to the copper:
1.
2.
3.
4.
3.00 – 5.00 mL of 16.0 M nitric acid
10.0 mL of 3.00 M sodium hydroxide
10.0 mL of 6.00 M sulfuric acid
x grams of aluminum
Using stoichiometric ratios, calculate the exact amount of each of the four
reactants (mL for solutions and grams for aluminum) that would react with your
initial amount of copper.
a. Based on your calculations, is any of the four reactants a limiting reactant?
b. If your answer is no, is there another limiting reactant in the experiment?
What is it?
Q2. Discuss why aluminum foil was used in the last step. Propose two additional
metals that would react with the copper solution to provide the copper metal.
Q3. Explain why silver and potassium would not be logically choices to use in the last
reaction of the experiment.
Q4. List at least two sources of experimental error that might lead to a mass of
reclaimed copper less than that originally used. Be specific.
Q5. List at least two sources of experimental error that might lead to a mass of
reclaimed copper greater than that originally used. Be specific.
Q6. In the lab, you calculated the percent yield of copper. Explain whether this result
supports or refutes the Law of Conservation of Mass. Explain your answer.
November 2008
Chemistry Teaching Center
Stony Brook University
Cycle of Copper Reactions Lab Exercise
The following is a protocol for the multi-step transformation of copper metal based upon
the following chemical transformations:
Cu(s) → Cu2+(aq) → Cu(OH)2 (s) → CuO (s) → Cu2+(aq) → Cu(s)
(1) Cu (s) + 4 H+ (aq) + 2 NO3-(aq) → Cu2+ (aq) + 2 NO2 (g) + 2 H2O (l)
(2) Cu2+ (aq) + 2 OH- (aq) → Cu(OH)2 (s)
(3) Cu(OH)2 (s) + heat → CuO (s) + H2O (g)
(4) CuO (s) + 2 H+ (aq) → Cu2+ (aq) + H2O (l)
(5) 3 Cu2+ (aq) + 2 Al (s) → 3 Cu (s) + 2 Al3+(aq)
Materials:
copper wire
12.0 M HNO3 (nitric acid)
6.0 M H2SO4 (sulfuric acid)
3.0 M NaOH (sodium hydroxide)
concentrated HCl (hydrochloric acid)
distilled water
aluminum foil
graduated cylinders (25 and 100 mL)
glass boiling beads
glass stirring rod
balance accurate to 0.01 g
microwave oven
250 mL Pyrex beakers
100 mL Pyrex beakers
watchglass
ring stand and iron ring with clamp
funnel
fast flow filter paper
litmus paper
graduated pipets (5 or 10 mL) with bulbs
Procedure:
**Safety Note: Goggles and lab aprons must be worn at all times while in the lab. Nonlatex or nitrile gloves must be worn whenever handling chemicals. Be very careful when
transferring acids or bases from their containers into your glassware.
*Note: All observations should be carefully recorded in your lab data packet.
November 2008
Chemistry Teaching Center
Stony Brook University
First Reaction: Cu (s) + 4 H+ (aq) + 2 NO3-(aq) → Cu2+ (aq) + 2 NO2 (g) + 2 H2O (l)
1. Mass the piece of copper wire and record its mass to the nearest 0.01g.
2. Cut the wire into smaller pieces, being careful not to lose any. Place into a clean,
dry 250 mL beaker.
Note: Next steps must be performed in the fume hood by an instructor.
3. As instructor performs the next steps; record your observations in your lab
packet.
4. The instructor will add 3 – 5 mL of concentrated nitric acid to the copper wire.
5. Reaction 1 will take place and when the copper has all reacted, approximately
10 mL of distilled water will be added to the beaker.
The following should be performed while waiting for your turn at the hood, or
before beginning step 5:
In your lab packet, using the mass of copper that you measured, calculate the
number of moles of copper that you placed into the beaker.
Second Reaction: Cu2+ (aq) + 2 OH- (aq) → Cu(OH)2 (s)
6. Using a pipet and pipet filler, add 10 mL of 3.0 M NaOH to the solution in the
beaker. Gently stir the solution with a stirring rod.
7. Test the acidity/alkalinity of the solution using litmus paper. DO NOT PUT
THE LITMUS PAPER INTO THE SOLUTION. Using the stirring rod, place 1
drop of solution onto a piece of litmus paper that has been placed onto a glass
slide.
8. If the solution is acidic, add additional NaOH a few drops at a time, with
stirring. Retest the solution with litmus paper after each addition of NaOH.
Repeat the addition of NaOH until your solution is slightly basic.
Third Reaction: Cu(OH)2 (s) + heat → CuO (s) + H2O (g)
**Note: Use “hot hands” mitts when handling hot beaker in microwave**
9. Dilute the solution by adding 80 mL of distilled H2O (use graduated cylinder to
measure) to the beaker and stir.
10. Add two or three boiling beads to the beaker and cover the beaker with a watch
glass. In microwave oven, heat the covered beaker for 20-seconds. Remove
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Chemistry Teaching Center
Stony Brook University
from the oven and stir.
11. Heat for another 20 seconds, then stir.
12. Repeat step 10.
13. Allow the solution to rest for a minute. Stir. If there is still any blue color
visible, heat for a fourth time, but only for 10 seconds. Stir again. If the solution
still looks blue, speak to an instructor and ask for assistance.
14. CuO forms as a solid black precipitate. Fill in appropriate data in lab packet.
15. Prepare the funnel by folding filter paper as demonstrated. Set up a ring stand
with an iron ring and clamp. Place an empty, clean, 250 mL beaker under the
ring and place funnel in iron ring so that the funnel will drain into the beaker.
Place filter paper in funnel and wet with distilled water using a wash-bottle.
16. Filter the solution by stirring the CuO mixture and slowly pouring into funnel.
Be sure to allow sufficient time for the funnel to drain, to avoid overflow.
Always allow at least 1 cm of space between top of funnel and the level of CuO
mixture.
17. Rinse beaker with distilled water and transfer any remaining solid into the
funnel.
18. Measure approximately 30 mL of distilled water into the 250 mL beaker.
19. Add 2 boiling beads and cover the beaker with a watch glass. Place the beaker
in the microwave, and heat the water for 20 seconds.
20. Rinse the residue in the funnel three times with 10 mL aliquots of warmed
distilled water (using pipet), allowing the water to drain through the filter before
adding additional water.
21. Keep filtered product, recover the boiling beads, and discard filtrate in waste
container that is in the hood, as per instructor’s directions. Record your
observations.
+
Fourth Reaction: CuO (s) + 2 H
(aq)
→ Cu2+ (aq) + H2O (l)
22. Place a clean, dry 250 mL beaker under funnel. Add 10 mL of 6 M H2SO4
drop-wise to the CuO in the funnel. If any solid remains on the filter paper, use
the dropper to take the filtrate out of the beaker and put it back into the funnel.
Note the details of the reaction in your lab packet.
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Chemistry Teaching Center
Stony Brook University
23. Using the distilled water bottle, wash the filter paper in the funnel with small
amounts of distilled water until no more blue is visible in the paper. Catch the
filtrate in the beaker containing the copper solution.
Steps 24 – 26 are optional. Check with instructor before proceeding.
24. Wearing gloves, carefully pour the copper sulfate solution into 25 mL graduated
cylinder and record volume of solution to appropriate number of significant
figures. Return solution to the beaker.
25. Using graduated pipet, remove a 2 mL aliquot of the acid solution and transfer
to a 50 mL beaker. Dilute the solution by adding 8 mL of cold distilled water.
Record volumes of acid solution and distilled water in lab packet. Transfer
solution to a spectrophotometer cuvette.
26. As demonstrated by instructor, prepare cuvette to be placed into the
spectrophotometer. Place cuvette into Spectronic 20 Spectrophotometer and
take Absorbance reading to appropriate significant figures. Record absorbance
in lab packet. After taking the reading, transfer the solution from the cuvette
back into the beaker containing the rest of the copper sulfate solution.
Fifth Reaction: 3 Cu2+ (aq) + 2 Al (s) → 3 Cu (s) + 2 Al3+(aq)
27. Using the provided chemical equations, determine the mass of aluminum foil
that will be needed for reaction (see data sheet for details).
28. Measure needed mass of aluminum foil (plus about 0.2 grams extra foil) using
the balance. Record the mass in your lab packet. Break the foil into 2 – 3
pieces.
Note: Next step must be performed in fume hood.
**Wear gloves when handling concentrated HCl (and of course, your goggles)**
29. Add aluminum foil pieces to the solution in beaker.
30. The instructor will add a few drops of concentrated HCl to the beaker. Stir
slowly with a glass rod while observing what happens to the aluminum foil.
Record observations in lab packet.
31. When the evolution of gas stops, if solution is still blue, add more aluminum
foil and a few more drops of concentrated HCl.
32. Fold a new piece of filter paper into cone shape as done previously. Determine
the mass of the filter paper and record it in your data packet.
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Chemistry Teaching Center
Stony Brook University
33. Write your initials on the filter paper using the permanent marker pen. Place
paper in funnel and wet with some distilled water.
34. When reaction has come to completion (no evolution of gas), filter out product
using a funnel and remember to put a beaker in place to catch the filtrate.
35. After product is filtered out, use the pipet to wash it with 20 ml of distilled
water in small increments. Discard the filtrate in the appropriate waste disposal
container.
36. Allow product to dry in a glass evaporating dish, using the drying oven as
needed.
37. Determine mass of product and filter paper and record the mass in your data
packet.
38. Calculate the percent yield for the series of reactions, as instructed in your data
packet.
Clean all glassware and return it to your station.
Dispose of gloves as instructed before leaving the lab.
Wash your hands before leaving the lab room.
November 2008
Chemistry Teaching Center
Stony Brook University
Cycle of Copper Reactions: Spectrophotometry Activity
Spectrophotometers, like the Spectronic 20 are used to measure the absorbance or percent
transmittance of a light beam of fixed wavelength (and frequency) by a solution, for
example, copper sulfate (CuSO4). Knowing the path length of the sample (l) and the
molar absorptivity (ε), one can find the concentration (c) of the solution by taking
absorption data, according to the Beer-Lambert Law:
A=ε•l•c
Absorption data are read as decimals between ∞ and 1. A reading of 1 means that all the
light that is shone on the cuvette is absorbed by the solution. A reading of “0” means that
none of the light was absorbed by the solution.
Part of the experiment we are going to perform involves finding the molar absorptivity of
copper sulfate, the product of one of the reactions in the activity. This can be
accomplished by taking absorption readings of copper sulfate solutions with varying
concentrations, and plotting the data on a graph. The slope of the “best-fit” line equals
the molar absorptivity.
Once a graph for the relationship between absorptivity and concentration of copper
sulfate has been established, the concentration of an unknown solution can be determined
if the absorptivity is known (assuming that the cuvette in use is the same for all readings
so that l is a constant, and that ε is the same for all copper sulfate solutions).
An absorption curve will be constructed using the absorption data of a number of copper
sulfate solutions. The solutions that you have prepared as a class will be analyzed. Once
the curve has been drawn, the absorption values for solutions of any concentration within
the range of the curve can be estimated. The curve will be utilized for this purpose
during the copper cycle experiment.
Activity: Preparation of Standard Curve for Copper Sulfate Solution
1) Obtain clean, dry cuvettes (resembling test tubes) and check each carefully for cracks,
scratches, residue, etc.
2) Prepare a “blank” cuvette by adding approximately 12 mL of distilled water to a clean
cuvette. Make sure that the wavelength on the Spectronic 20 is set to 640 nm. Turn the
left adjustment knob on the front of the Spectronic 20 until the needle is aligned at the
infinity (∞) mark. Insert the blank cuvette and close the lid. Turn the right adjustment
knob until the meter reads “0”. Remove the blank cuvette. The Spectronic 20 is now
calibrated. Note: Do not touch the adjustment knobs or change the wavelength once
the machine is calibrated.
3) Take absorption readings of each copper sulfate solution, one at a time, by adding
approximately 12 mL of solution to clean, dry cuvettes. Insert the cuvette (as instructed)
into the Spectronic 20 and close the lid. Once the needle has stopped moving, determine
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Chemistry Teaching Center
Stony Brook University
the absorption to the appropriate number of significant figures and record below. Repeat
this for each solution.
Concentration
Absorption
4) Construct an absorptivity curve on the provided graph paper using the data from
step 3. Place the independent variable (concentration) on the x-axis, and the
dependent variable (absorbance) on the y-axis. Be sure to use the appropriate scale,
and draw your graph so that it takes up at least two-thirds of the entire page. Draw a
“best-fit” line and determine its slope. This slope equals the molar absorptivity of the
copper sulfate solutions.
5) Determine the slope of the line.
November 2008