Reactions of Copper

Description

Copper metal is dissolved in nitric acid. The copper in the copper nitrate solution is converted into copper hydroxide which, upon heating, is converted into copper oxide. The copper oxide is dissolved in acid, and the resulting solution is treated with zinc metal to produce copper metal. This is not performed as a quantitative experiment.

Go to Top

Concentrated nitric acid, dilute sodium hydroxide, and dilute sulfuric acid are corrosive. Nitrogen (IV) oxide is toxic. Burns are possible from the heating device. Injuries are possible as the result of centrifugation.

Go to Top

• Wear gloves when handling concentrated nitric acid. Wear eye protection at all times. Wash spills immediately using large amounts of water. Check safety showers and eye wash fountains.
• Add nitric acid to copper under a hood.
• Check to be certain that the heating device has cooled before touching.
• Balance all centrifuge loads. Do not touch a spinning centrifuge. Make sure that the centrifuges do not present electric shock hazards.

Go to Top

1. Wear gloves. Roll strands of copper filament into a small sphere about the size of a small green pea. Place the resulting piece of copper in a 100-mm test tube. Support the test tube in a small beaker.
2. Place the beaker in a hood. Wear gloves. Fill a thin-stemmed polyethylene transfer pipet with 0.4 mL concentrated nitric acid. Add 5 drops of concentrated nitric acid to the copper in the test tube. Note evidence for reaction.
3. Wait until the reaction ceases and no solid is visible in the test tube. Use a plastic wash bottle to fill the test tube about 1/3 full with water. Note evidence for reaction.
4. Place a glass rod in the test tube. Remove the glass rod and touch the tip to a piece of red litmus paper supported on a watch glass.
5. Note the color.
6. Add slowly some 3 M NaOH solution to the test tube. Stir. Note any evidence for reaction.
7. Use the glass rod to remove a sample of the resulting slurry.
8. Test the slurry with the litmus paper by touching the rod to the paper. Continue adding sodium hydroxide until the slurry is basic and turns red litmus paper blue.
9. Place 100 mL of tap water in a 250-mL beaker. Place the beaker on a hot plate. Heat. Place the test tube in the beaker.
10. Use the stirring rod to stir occasionally. After a few minutes, the bluish copper (II) hydroxide is converted into black copper(II) oxide.
11. Set the test tube in a support beaker overnight so that the copper(II) oxide can settle. Centrifuge the tube if a centrifuge is available. (Follow carefully all centrifuge precautions including balancing the load and never touching a moving centrifuge rotor).
12. Wait until the solid material has settled as the result of either centrifugation or standing overnight. Use an empty thin-stemmed polyethylene transfer pipet to remove the supernatant fluid from the solid.
13. Place 3 mL of 3 M H₂SO₄ in a thin-stemmed polyethylene transfer pipet. Add the sulfuric acid to the test tube. Place a glass stirring rod in the test tube. Stir until the solid dissolves.
14. Add one small spatula full of granulated zinc metal (2 green peas) to the test tube. Note any evidence for reaction.
15. Set the tube aside overnight. After one day, observe the resulting material in the tube.

Go to Top

Name ___________________________ Class ________

Teacher__________________________

DoChem 054 Reactions of Copper

Watch the movie and answer these questions.

1. In what ways is the solid in the tube at the end of the experiment similar to the solid copper starting material? What differences are apparent?
2. Write balanced chemical equations to account for the observations during each part of the procedure where chemical changes are observed.
3. Suggest a way to determine when the reduction of the copper ion to copper metal by zinc metal is complete.

Go to Top

Purpose

To illustrate a series of chemical reactions of copper.

Go to Top

(for ten students working in pairs)

• 2 g fine strands of copper metal
• 5 13- x 100-mm test tubes
• 5 100-mL beakers
• 5 250-mL beakers
• hot plate
• 5 15-cm glass rods
• 15 thin-stemmed polyethylene transfer pipets
• 15 mL 3 M NaOH
• 15 mL 3 M H₂SO₄
• 2.5 mL concentrated nitric acid
• 5 g granular zinc metal
• hood
• 10 pairs of gloves

Go to Top

Do not perform this experiment unless hoods are available.

Go to Top

Teacher preparation: 30 minutes

Class Time: 3 consecutive periods

• 45-50 minutes first period
• 15 minutes second period
• 5 minutes third period (Observe reaction)

Go to Top

• Be extremely cautious when disposing of concentrated nitric acid. Dilute the acid by adding it to a large volume of water at the hood. Neutralize the acid with base, and dispose of at the sink.
• Treat excess dilute sulfuric acid by adding to water. Treat excess dilute sodium hydroxide by adding to water. Slowly mix these diluted solutions together. Test the acidity of the resulting solution, and neutralize. Discard the resulting solution at the sink.
• The solid copper, excess zinc metal, and used litmus paper may be disposed of with ordinary solid trash.

Go to Top

Closure Questions:

1. In what ways is the solid in the tube similar to the solid copper starting material? What differences are apparent?
2. Write balanced chemical equations to account for the observations during each part of the procedure where chemical changes are observed.
3. Suggest a way to determine when the reduction of the copper ion to copper metal by zinc metal is complete.

Answers to Closure Questions:

1. The solid copper has a color similar to the original. The physical appearance (lack of shine, granular) are strikingly different.
2. 3 Cu + 8 H⁺ + 2 NO₃^- --> 3 Cu²⁺(aq) + 2 NO + 4 H₂O

   2 NO + O₂ --> 2 NO₂

   Cu²⁺(aq) + 2 OH^-(aq) --> Cu(OH)₂

   Cu(OH)₂ --> CuO + H₂O

   CuO + 2 H⁺(aq) --> Cu²⁺(aq) + H₂O

   Cu²⁺(aq) + Zn --> Cu + Zn²⁺(aq)

   Zn + 2 H⁺(aq) --> Zn²⁺(aq) + H₂(g)

3. The disappearance of the blue color indicates the completion of the reaction.

Go to Top

• Metallic copper reacts with concentrated nitric acid according to the chemical equations:

  3 Cu(c) + 8 H⁺(aq) + 2 NO₃^-(aq) --> 3 Cu²⁺(aq) + 2 NO(g) + 4 H₂O

  Cu(c) + 4 H⁺(aq) + 2 NO₃^-(aq) --> Cu²⁺(aq) + 2 NO₂(g) + 2 H₂O

• Copper has a distinct color; it is not like the silvery metals. Copper(II) compounds are usually colored blue. NO is a colorless gas. In contact with air, NO reacts very rapidly to produce brown NO₂:

  2 NO + O₂ --> 2 NO₂

• When treated with a source of hydroxide ion, copper(II) forms insoluble, gelatinous, bluish copper(II) hydroxide:

  Cu²⁺(aq) + 2 OH^-(aq) --> Cu(OH)₂

• When heated, copper(II) hydroxide loses water to produce copper(II) oxide:

  Cu(OH)₂ --> CuO + H₂O

• In acidic aqueous medium, copper(II) oxide dissolves producing blue Cu2+(aq) :

  CuO + 2 H⁺(aq) --> Cu²⁺(aq) + H₂O

• Metallic zinc reacts with aqueous copper(II) ions to produce copper metal and aqueous zinc (II) ions:

  Cu²⁺(aq) + Zn --> Cu + Zn²⁺(aq)

• Excess zinc metal reacts with acid:

  Zn + 2 H⁺(aq) --> Zn²⁺(aq) + H₂(g)

Go to Top

• copper
• reaction
• redox
• oxidation
• reduction
• metal
• dissolve
• precipitate
• acid
• base
• neutralization

Go to Top