Cu Again: A Copper Cycle Lab

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Cu Again: A Copper Cycle Lab
This lab will take you through a series of reactions, starting with copper as a reactant in the first
reaction and ending with copper as a product in the last reaction. The copper you collect at the end
may look different but this is only because it is not cleaned and polished. If you work carefully and
take care to rinse the product thoroughly, your final product will closely resemble the original copper
(though you may need to hammer it into a wire to see the resemblance)!
Purpose
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Use careful lab skills to carry out the entire series of reactions safely
Predict the products you should obtain at each step
 Check chemical literature for the expected physical properties of the products
(color, state, solubility in water)
Recover as close to 100% as possible of the original copper
Use stoichiometry to calculate the mass of aluminum that should be used in the last
step
Calculate percent recovery (like percent yield) for the overall process
Safety and Data Recording
o ALWAYS wear goggles and apron!!!!!!!!!!!!!!
o Wash hands if chemicals get on you. Many of them are corrosive or strongly acidic or
basic.
o Record ALL masses to correct precision and record units with measurements.
o Make DETAILED observations. Note any color, temperature or state changes that
occur during each reaction.
Procedures
NOTE: All reactions will be carried out in a test tube. The numbers in parentheses before each
solution represent the concentration used.
Reaction 1
This reaction must be carried out under a fume hood. A noxious brown gas called nitrogen
dioxide is a side product of the reaction. Note that the NO2 will not be accounted for in your
equation since it is a result of the excess acid decomposing.
Dissolve no more than 0.25 g copper metal in 2.5 mL (6M) nitric acid.
Observations:
Reaction Type:
Balanced Equation (include symbols):
Expected physical properties of products (from chemical literature):
Reaction 2
The non-gaseous product from Reaction 1 is the first reactant for this reaction.
To the product solution, add 1.5 mL (6M) sodium hydroxide. DO NOT MIX!!
Observations:
Reaction Type:
Balanced Equation (include symbols):
Expected physical properties of products (from chemical literature):
Reaction 3
If the test tube is not ½ full, add distilled water until it is. This water is NOT a reactant. ONLY
the copper compound formed in Reaction 2 will be a reactant for this reaction. The other
compound and water are bystanders and will be rinsed away at the end of this step.
Clamp the test tube in a hot water bath, submerging it as low as possible without letting the bottom
touch the beaker. Heat and watch for changes. When the change is nearly complete, stir with a glass
stirring rod until the change is complete. Remove the test tube and cool it by running the outside
under cold water. Allow the contents to settle, then carefully pipette as much of the clear solution as
possible away from the test tube (the clear solution contains the extra bystander solution to be
discarded).
*Unplug the hotplate, but do not remove the water (in case you need it during the last step).*
Observations:
Why would it be difficult to separate out the bystander solution at this step?
Reaction Type (remember, only one reactant!):
Balanced Equation (include symbols):
Expected physical properties of products (from chemical literature):
Reaction 4
To the remaining solid product, slowly add (6M) hydrochloric acid until all of the solid disappears. Do
not add excess acid once the reaction is complete.
Observations:
Reaction Type:
Balanced Equation (include symbols):
Expected physical properties of products (from chemical literature):
Reaction 5
ONLY the copper compound formed above will react with the added reactant in this step. If
the test tube is not approx. ¾ full, add distilled water until it is. Water is not a reactant, it is
only diluting the solution.
Obtain a piece of Aluminum wire and record its mass. Place the aluminum in the solution and gently
mix. The reaction is complete when the solution is colorless. (Bubbling may still be present due to a
side reaction.) ONLY if this reaction is proceeding slowly, you may clamp the test tube in the warm
water left over from Reaction 3.
Observations:
Reaction Type:
Balanced Equation (include symbols):
Expected physical properties of products (from chemical literature):
Recovery of Product
Carefully decant (pour off) the liquid into a beaker. Make sure to keep the solid product in the test
tube at all times. Once you have successfully separated any liquid from the solid, the liquid may be
discarded. Use a metal scoop to scrape all of the brown solid from the extra aluminum wire into the
test tube. Rinse and scrape the aluminum until as much of the brownish solid as possible is left in the
test tube. Set the aluminum aside.
Cleaning of Product
Add about 10 mL of distilled water to the solid in the test tube. Stir and allow the solid to settle.
Decant the water from the test tube into a beaker. This process is called “washing”. Wash the
product 1-2 more times then scrape it onto a piece of pre-weighed filter paper to dry overnight. (Mark
your name on the filter paper in pencil.) Once dry, record the mass of the copper product.
Analyze Aluminum
Clean the remaining aluminum wire from Reaction 5 with a test tube brush. Dry and record the new
mass of aluminum. Return the aluminum and any other left over chemicals to the teacher.
Make sure to clean all lab equipment with soap and water and wash your hands. Make sure
the hot plate is cooled before returning it to the cabinet. DO NOT TAKE OFF YOUR GOGGLES
UNTIL ALL CHEMICALS ARE PUT AWAY AND ALL GLASSWARE IS WASHED AND DRIED.
DATA REPORTING AND ANALYSIS
1. On a separate piece of paper, create an organized data table to show your results.
2. Calculate the percent recovery of the overall process (just like percent yield). Explain where the
numbers came from.
3. Use the calculated percent recovery and experimental observations to comment on the accuracy
of the processes used. Describe at least one error SPECIFIC to this experiment that could account
for YOUR discrepancy (you probably did not get a perfectly clean 100% yield).
4. For this question, we’ll assume all the copper atoms from the beginning were still present in the
last step. Calculate the number of moles of copper you started with.
Moles Cu
Verify that the # moles of copper from Reaction 1 equals the # moles of copper (II) chloride in
Reaction 5. Then, write the balanced equation for Reaction 5. Using stoichiometry, determine the
moles, then mass of aluminum that should have been consumed in this step. Account for any
discrepancies in your experimental data.
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