Purpose:
To observe the copper metal-nitric acid reaction and through a series of reactions observe the precipitation of copper(II) hydroxide, the conversion of solid copper(II) oxide, the change to aqueous copper(II) sulfate, and finally the change back again to copper metal.
Background:
In this experiment we will cycle the element through a series of chemical reactions. Copper is a soft metal with a characteristic color that we often call “copper-colored”, a bright orange-brown color. Copper is relatively inert chemically; it does not readily air oxidize (react with oxygen in air) and is not attacked by simple mineral acids such as hydrochloric or sulfuric acid.
The Dissolution of Copper Metal
Cu(s) + HNO
3
(aq)

Cu(NO
3
)
2
(aq) + NO
2
(g) + H
2
O(l)
Copper readily reacts with substances that are strong “oxidizers” (chemists call these substances strong oxidizing agents). In this experiment aqueous nitric acid is the substance that oxidizes copper metal. Copper(II) nitrate will be produced and since it is a water soluble salt, will produce a blue solution. Nitrogen dioxide, a dense, red-brown gas will also be produced. The solution remains acidic because of an excess of nitric acid used for the reaction.
The Precipitation of Copper Ion from Solution
Cu(NO
3
)
2
(aq) + NaOH(aq)

Cu(OH)
2
(s) + NaNO
3
(aq)
The copper(II) nitrate solution made in the first part of the experiment is made basic with sodium hydroxide. This results in the precipitation of copper(II) hydroxide, a light blue precipitate. The sodium nitrate produced in the reaction is a water soluble, colorless salt and will remain in solution.
Conversion of Copper(II) Hydroxide to a Second Insoluble Salt
Cu(OH)
2
(s)

CuO(s) + H
2
O(l)
Copper(II) hydroxide dehydrates with heat to form black, insoluble copper(II) oxide.
Dissolution of Copper(II) Oxide
CuO(s) + H
2
SO
4
(aq)

CuSO
4
(aq) + H
2
O(l)
Copper(II) oxide dissolves in aqueous sulfuric acid to form a sky blue solution due to the formation of the water-soluble salt, copper(II) sulfate.
Reformation of Copper Metal
CuSO
4
(aq) + Zn(s)

Cu(s) + ZnSO
4
(aq)
The copper cycle is completed in this experiment with the addition of zinc metal to the copper(II) sulfate solution. In this reaction, because zinc is a more reactive metal than copper, it displaces copper from the copper(II) sulfate solution, forming copper metal and water-soluble zinc sulfate.
Zinc also reacts with sulfuric acid; therefore, when zinc is added to the copper(II) sulfate solution, a reaction between zinc metal and sulfuric acid also occurs producing hydrogen gas and additional zinc sulfate.

Equipment:
Laboratory balance
250-mL Beaker
Glass stirring rod
25-mL Graduated cylinder
Safety goggles
Hot Plate
400-mL Beaker
Beaker tongs
100 mL Graduated cylinder
Boiling chips
Chemicals:
Copper metal
6 M Sodium hydroxide (NaOH)
6 M Hydrochloric acid (HCl)
Procedure:
6
1
M
M
Nitric acid (HNO
Sulfuric acid (H
Zinc metal
2
3
)
SO
4
)
1. Wear safety goggles throughout the experiment. Obtain and label a 250-mL beaker with a permanent ink pen. Weigh and record the mass of the clean, dry 250-mL beaker. Set the balance to zero with the beaker on it and cut approximately 1.50 grams of copper wire into the beaker.
Record the exact mass of copper. Make sure the copper all sets on the bottom of the beaker.
2. Place the beaker and copper in the fume hood. Pour approximately 20.0 mL of 6 M nitric acid
into your 25-mL graduated cylinder and add the acid slowly to the copper. Leave the beaker in the fume hood until all of the solid copper metal and the colored fumes have disappeared. Heat the beaker gently if necessary. Avoid breathing the fumes. They are TOXIC! Record your observations.
3. Remove your beaker from the fume hood. Fill a 600-mL beaker about 1/3 full of cold tap water. Place the smaller 250-mL beaker, containing the solution, into the larger beaker to cool the mixture for the next reaction. Make sure the solution is cool before proceeding to the next step.
4. Measure 20 mL of 6 M sodium hydroxide solution into a 25-mL graduated cylinder.
CAUTION! Slowly pour the sodium hydroxide solution into the blue solution. Stir gently with a glass stirring rod after all of the sodium hydroxide has been added. Record your observations.
5. Add about 100 mL of distilled water to the mixture from step 4. Add three boiling chips to the solution and begin to gently heat the beaker and its contents until it boils. Continue to slowly heat the mixture to keep the mixture boiling gently until all of the solid changes to the same dark color. Allow the mixture to cool. Decant the liquid being careful not to lose any of the solid.
Wash the solid in the beaker with about 100 mL of distilled water. Allow the beaker to stand until all the solid settles. Decant again, leaving all the solid in the beaker. Record your observations.
6. Add 40.0 mL of 1 M sulfuric acid to the solid. Stir the mixture with a glass stirring rod.
Record your observations.
7. Find the mass of a strip of zinc metal. Place the zinc strip in the blue colored solution. Warm the solution until it starts to boil. Set the beaker aside and allow it to stand for approximately 40 minutes. Record your observations.
8. Decant the solution from the solid copper in the beaker. Wash the copper with distilled water and decant. Pick out the boiling chips and return them to the chemical and supply table. Be careful to retain all of the copper in the beaker.
9. Add about 10 mL of 6 M hydrochloric acid to the mixture and warm it to dissolve any pieces of zinc left. Wash the copper and decant with distilled water several more times. Place the beaker in the oven to dry.
10. Weigh the beaker and the dry copper. Place the copper in the waste beaker in the back of the room.