Reduction of Copper(II) Oxide

Description

Black copper oxide is reduced to form copper metal (with its characteristic appearance) using methane gas. The reaction is clean and stoichiometric.

Go to Top

1. Set up the apparatus behind a safety shield.
2. Prepare a wire from which to hang a test tube. Wrap a loop of wire around the top of a 16-mm test tube near the lip. Shape the other end of the wire into a loop. This loop should be about 3-4 cm from the tube. Determine the mass of a test tube by hanging it from the loop of wire attached to the balance hook. Weigh a clean, dry test tube. Record the mass.
3. Students record the mass.
4. Add 1 gram to the mass on the balance.
5. Add about 1 gram copper (II) oxide with a metal scoop so that as little as possible of the powder gets on the side of the test tube.
6. Continue adding copper (II) oxide until the balance swings up.
7. Reweigh the test tube and powder. Record the mass.
8. Insert the glass tube connected to the methane gas supply carefully so that it does not touch the powder. You may want to hold it during the demonstration or clamp it to a support stand. The glass tube should extend far into the test tube, but not touch either the solid in the test tube or the test tube itself.
9. Light a match and turn on the source of methane gas for the glass tube inserted into the test tube. The flame should be about 5 cm (2 inches) high at the mouth of the test tube.
10. Light a Bunsen burner and adjust it for a hot flame. Move the burner under the sample. It may then be moved back and forth to provide even heating.
11. The sample is black to brown before heating.
12. Heat the exterior of the test tube to a high temperature with the Bunsen burner for about 5 to 7 minutes or until copper color appears in the material in the test tube.
13. Turn off the Bunsen burner, but keep the methane flowing through the inside of the test tube until the test tube cools down (about 5 minutes).
14. Cautiously test the temperature.
15. (Because of the heat released at the top of the tube when the methane is burning, the tube will not cool to room temperature. Once the gas is turned off, wait until the tube does cool to room temperature.)
16. Once cooled, turn off the methane.
17. Reweigh the test tube and material remaining. Record the mass.

Go to Top

Name ___________________________ Class ________

Teacher__________________________

DoChem 020 Reduction of Copper(II) Oxide

Mass empty tube =

Mass tube plus oxide =

Mass tube after reduction =

What might happen if the natural gas supply passing over the copper oxide is turned off a few minutes before the external heat is turned off?

1. Write a balanced chemical equation to describe the reaction between methane and copper(II) oxide.
2. Use the sample data here. Assume that the formula of copper(II) oxide is CuO. For the sample size taken, predict the mass of copper that should remain after reaction.
3. Compare the predicted mass of copper remaining with that actually observed. Suggest possible reasons for discrepancies.

Go to Top

Name ___________________________ Class ________

Teacher__________________________

DoChem 020 Reduction of Copper (II) Oxide

Watch the movie.

Use this data for your calculations.

Mass empty tube = 41.80 g

Mass tube plus oxide = 43.00 g

Mass tube after reduction = 42.78 g

What might happen if the natural gas supply passing over the copper oxide is turned off a few minutes before the external heat is turned off?

1. Write a balanced chemical equation to describe the reaction between methane and copper (II) oxide.
2. Use the sample data here. Assume that the formula of copper (II) oxide is CuO. For the sample size taken, predict the mass of copper that should remain after reaction.
3. Compare the predicted mass of copper remaining with that actually observed. Suggest possible reasons for discrepancies.

Go to Top

Purposes

• To observe a chemical reduction.
• To illustrate quantitative relationships.

Go to Top

• Bunsen burner
• hose with bent glass tubing; tubing inserted into rubber stopper or cork for clamping
• 25 x 200 mm test tube (16 x 100 mm okay)
• wire to suspend tube for weighing
• 1 g finely powdered copper (II) oxide
• source of methane gas
• 2 single-buret clamp
• 2 support stand
• balance
• may need y-tubes and clamps to provide sufficient gas outlets
• safety shield

Go to Top

• The experiment has not been checked with propane or butane sources.
• An interesting variation is to use a tightly fitting two-holed rubber stopper for the tube. Insert a long glass tube through one hole so that is comes within 1 cm of the bottom of the test tube and extends 5 cm to the other side of the stopper. Insert a 10-cm length into the other hole so that 5 cm of tubing protrudes. Connect rubber tubing from the gas source to the longer glass tube. Connect rubber tubing from the Bunsen burner to the short glass tube. Turn on the gas. The gas first flows over the oxide, and then flows out through the Bunsen burner. Wait 15 seconds. Light the gas. When the reaction is complete, remove the burner, and allow the reaction test tube to cool while the gas burns in the Bunsen burner.
• Y-tubes or T-tubes and suitable clamps may be needed to provide enough gas outlets in laboratories where these are not available.

Go to Top

First-time materials set-up: 45 minutes

Teacher preparation: 15 minutes

Presentation: 40-45 minutes

Go to Top

Natural gas is flammable and potentially explosive. Hot glassware can cause burns. Bending glassware and inserting glass tubing through rubber stoppers can lead to severe cuts.

Go to Top

• Use a safety shield.
• Ignite escaping gas after a 15 second wait. Be careful handling hot glassware; use fingers to sense whether glassware has cooled to room temperature before grasping. Do not use plastic coated clamps.
• To insert tubes into stoppers, use fire-polished glass (i.e., glass heated to remove sharp edges.) Use a lubricant such as glycerin on the glass and the stopper. Wrap the glass and the stopper in a cloth towel. Slowly, with minimal pressure, twist the glass into the stopper.

Go to Top

Reuse the same test tube from year to year. The solid may be disposed of with ordinary solid waste.

Go to Top

Presentation Questions:

• What might happen if the natural gas supply passing over the copper oxide is turned off a few minutes before the external heat is turned off?
  • The copper metal formed by reduction might (will) reoxidize to copper oxide if it comes in contact with oxygen from the air.

Go to Top

Mass empty tube = 41.80 g

Mass tube plus oxide = 43.00 g

Mass tube after reduction = 42.78 g

Go to Top

The mass of copper (II) oxide is:

43.00 g - 41.80 g = 1.20 g

The mass of solid remaining is:

42.78 g - 41.80 g = 0.98 g

If all of the remaining material were copper, there would be:

0.98 g Cu x (1 mol Cu/ 63.54 g Cu) =0.0154 mol Cu

If all of the lost mass were due to oxygen, there would be:

1.20 g - 0.98 g = 0.22 g O, and 0.22 g O x (1 mol O/ 16.00 g O) = 0.0138 mol O

The mole ratio of Cu to O is:

0.0154 mol Cu/ 0.0138 mol O = 1.16

Go to Top

Closure Questions:

1. Write a balanced chemical equation to describe the reaction between methane and copper(II) oxide.
2. Use the sample data here. Assume that the formula of copper(II) oxide is CuO. For the sample size taken, predict the mass of copper that should remain after reaction.
3. Compare the predicted mass of copper remaining with that actually observed. Suggest possible reasons for discrepancies.

Answers to Closure Questions:

1. CH₄ + 3CuO --> CO + 2H₂O + 3Cu
2. The molar mass of CuO is:

   1 mol Cu x (63.54 g Cu/1 mol Cu) = 63.54 g Cu

   1 mol O x (16.00 g O/ 1 mol O) = 16.00 g O

   63.54 g Cu + 16.00 g O = 79.54 g CuO

   1.20 g CuO x (63.54 g Cu/79.54 g CuO) = 0.959 g Cu

   For CuO, the predicted mass of Cu remaining is 0.959 g

3. The observed mass is 0.98 g Cu, and the predicted mass is 0.96 g Cu. This difference can be due to weighing error or insufficient heating.

Go to Top

• redox
• reduction
• reaction
• mole
• mole relationship
• balanced equation

Go to Top