A Colorful Cycle of Copper Reactions
Prelab: read the entire laboratory before beginning.
Create a data table for your information.
Create a flow chart of expected steps.
Create a hypothesis.
Get stamped prior to starting the laboratory.
Prelab Questions
1. How to you perform an error calculation.
2. What are the primary safety concerns in the laboratory. In
other words of what do you need be aware?
3. How could this laboratory be applied to real life?
Ask your instructor to explain any aspects of the procedures that you
do not understand.
As you work, keep full, legible records of your observations in the
proper sections of your printed Report Form.
Preparation
At your bench, start two hot water baths for later use:
1) Determine the equipment needed for the section on which you are
working. Do not gather equipment until you are approaching the
end of one section and are ready to proceed to the next one.
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2) Keep an eye on the clock as this is a multiple day laboratory and
you will need to complete the data gathering to the next to last
section in three days.
3) Put 150 mL of tap water in a 400-mL beaker on a hot plate. Keep
the water at a simmer. Add water from time to time to keep the
level between 100 and 150 mL. You will use this bath to heat a
flask during part 3.
4) Start a smaller hot-water bath of about 40 mL distilled water in a
100-mL beaker. You will use this hot distilled water to wash a
filtered residue in part 3.
NOTE: In all operations, be careful to avoid losses of even small
amounts of solids or liquids containing copper compounds. If your lab
technique is good, you will be rewarded in part 5 with a high percent
recovery of the copper with which you start in part 1.
Part 1: Converting copper metal to aqueous Cu2+ ions
WARNING: Concentrated nitric acid is corrosive and causes severe
burns. Handle with care. Dilute and wash up spills with plenty of
water.
1. Clean some copper wire with steel wool, and then cut a 3- to 4-cm
piece of wire.
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2. Weigh the wire to the full precision allowed by your balance, and
record its mass.
3. Make a flat coil of the wire, and place it in a dry 125-mL Erlenmeyer
flask.
4. In the fume hood, carefully add 1.5 to 2 mL of concentrated (6 M)
nitric acid (HNO3), to cover the copper wire in the flask.
5. Gently warm the flask to speed the reaction if needed, but don’t get
the flask hot.
6. If any copper remains undissolved after 5 minutes, carefully add
another 0.5 to 1 mL of nitric acid and continue warming.
7. Finally, still in the hood, dilute the resulting solution with about 30
mL of deionized water. Now you may remove the flask from the
hood, and continue working at your lab bench.
Part 2: Precipitating copper (II) hydroxide
WARNING: Concentrated sodium hydroxide is corrosive and causes
severe burns. Handle with care. Dilute and wash up spills with plenty
of water.
1. Add 6 M sodium hydroxide (NaOH) to the flask slowly, with
thorough mixing, until a precipitate forms.
2. Continue adding small amounts of NaOH until the solution is basic
to litmus paper.
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3. Then add two additional drops of NaOH and mix well.
Part 3: Converting copper (II) hydroxide to copper (II) oxide
1. Increase the volume of solution in the flask to about 100 mL by
adding deionized water.
2. Use a screw clamp to suspend the flask containing the reaction
mixture in your large hot water bath.
3. Heat for 4 or 5 minutes after the temperature rises to near 100 oC,
stirring constantly (glass stirring rod), and then remove from heat
and allow to cool.
4. Next, fold a piece of filter paper as shown in Figure 1.
5. Place the paper in a filter funnel mounted in a utility clamp attached
to a support stand.
6. Place another Erlenmeyer flask under the funnel to collect the
filtrate.
7. Use distilled water from your wash bottle to wet the filter paper.
Press the top edges of the filter paper against the sides of the
funnel to form a seal. Avoid touching the wet filter paper—even a
touch can tear it and allow the filtrate to pass through.
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8. When the 125 mL flask is cool enough to handle, filter the contents,
using another flask to collect the colorless filtrate. Do not allow the
liquid level in the filter to rise above the top of the paper.
9. Transfer the last traces of the solid CuO from the flask into the
funnel, using a stream of distilled water from the wash bottle.
10.
Wash the residue on the filter paper three times, using 5-mL
portions of hot distilled water from your smaller water bath.
11.
Use beaker tongs to handle the hot beaker when pouring the hot
water.
12.
Allow each portion of hot water to drain through the filter paper
into the flask before adding the next portion.
13.
Retain the solid CuO on the filter paper for use in Part 4.
Part 4: Dissolving copper (II) oxide to form aqueous Cu2+ ions
WARNING: Sulfuric acid solution is toxic. Handle it carefully. Prevent
eye, skin, and clothing contact. If you spill any acid, immediately
notify your laboratory instructor.
1. Place a clean 250-mL beaker under the funnel stem.
2. Dissolve the CuO on the filter paper by allowing about 15 mL of 1M
H2SO4 solution to pass through the CuO and the filter paper.
3. Allow the acid solution to drain through the funnel into the 250-mL
beaker.
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4. If the solid does not completely dissolve, pour the liquid from the
beaker back into the funnel, using a second clean beaker to collect
the filtrate.
5. Repeat this procedure until the solid has completely dissolved.
6. Wash the empty filter paper with distilled water from the wash
bottle. Collect the water in the 250-mL beaker containing the acid
solution. Combine all the acid solution in one beaker.
7. Rinse the second beaker with 10 mL of distilled water and add to
the acid solution. Retain acid solution for use in Part 5.
Part 5: Precipitating Cu2+ ions as copper metal
WARNING: Concentrated hydrochloric acid is corrosive and causes
severe burns. Handle with care. Dilute and wash up spills with plenty
of water.
1. In the hood, add 0.25 to 0.3g of magnesium metal to the beaker
containing the blue-green solution of Cu2+ ions, and heat the
solution to near boiling on the hot plate.
2. Using a glass stirring rod, agitate the solution to speed the
precipitation of copper granules. Continue stirring and heating until
the solution is colorless.
3. If bubbling stops but the solution is still blue, add additional
magnesium to completely precipitate the copper and eliminate the
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blue color of the supernatant. Then decant the supernatant into a
waste container.
4. Wash the copper metal in the beaker with two portions of 20 mL
deionized water.
5. Allow the solids to settle and decant after each wash.
6. In the hood, carefully add small amounts of 6 M hydrochloric acid
(HCl) to completely dissolve any remaining magnesium.
7. If bubbling stops, but silvery Mg is still present, add 1-2 drops more
6 M HCl.
8. Allow the copper granules to settle, and then decant the
supernatant liquid into a waste container. Wash the copper granules
three times with 25 mL of warm deionized water.
9. Pre-weigh a piece of filter paper and label as to period and tem
number.
10.
Set up a filter apparatus as before and filter the copper solid
from the supernatant liquid.
11.
Place filter paper in fume hood under the lamps and allow drying
at least 48 hours.
12.
Determine if the filter paper/copper solid is dry, if it is mass and
calculate the resultant amount of copper. If not, let it dry for
another day.
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Use the percentage error calculation and determine the amount of
copper recovered.
Your true will be the original measured amount of copper wire.
Your observed value will what you measured at the end of the lab.
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