Chemistry Name

Laboratory Demonstration

Experiment 8 (Reduction of Copper (II) Oxide)

Background Information

In this experiment, a sample of pure copper oxide, will be reduced to metallic copper, Cu, by heating the CuO in the presence of a reducing agent, Natural Gas or Methane, CH4. The equation below represents the reaction that takes place.

4 CuO(s) + CH4 (g) ® 4 Cu (s) + CO2 (g) + 2 H2O (g)

Since all gaseous products escape the system, only solid copper metal should remain in the test tube. We should be able to use experimental data to determine the percentage composition of the copper oxide sample and determine the empirical formula for the compound.

Pre-Lab Questions:

Copper cations can be Cu1+ or Cu2+ resulting in two possible empirical formulas when combined with oxide, O2-. Identify the percent composition of copper for each possible formula.

Copper (I) oxide, Cu2O Copper (II) oxide, CuO

%Cu = % Cu =

Procedure

  1. Put on a lab apron and safety goggles.
  2. Determine the mass of a clean, dry 18 x 150 mm test tube to the nearest 0.01 g. Roughly weigh about 2.0 g of copper (II) oxide, CuO, on a piece of paper. Assemble the equipment needed to conduct this experiment as shown by your instructor.
  3. Roll a piece of paper into a tight cylinder and place it in the previously weighed test tube. Transfer the CuO sample to the bottom of the test tube through the paper cylinder. Carefully remove the paper cylinder, leaving the CuO confined to the bottom of the test tube. Determine the mass of the test tube containing the CuO sample to the nearest 0.01 g. Record the mass in a data table.

4.  Complete the apparatus setup. Adjust a slow flow of burner gas through the glass tube (do not blow the CuO around!) and with a match promptly ignite the gas at the mouth of the test tube. Adjust the gas flow to obtain a 4-cm-high flame at the tube mouth. Caution: Keep clothes and hair away from the test tube mouth.

  1. Now light and adjust the flame of a Bunsen burner to obtain the hottest possible flame. Heat the CuO by slowly moving the burner flame under the end of the test tube. Continue to heat the copper (II) oxide until it is fully converted to metallic copper. (How can you determine this?) The reaction usually takes about 5 minutes. Carefully heat the wall of the test tube to “chase out” any condensed moisture, which is another product of the reaction.
  2. Remove the Bunsen burner, but allow the gas to continue to flow through the glass tube and to burn at the tube mouth. Wait 5 minutes, or until the test tube is cool to the touch. When the tube has cooled, turn off the gas flowing to the tube. There should no longer be a flame at the mouth. Extinguish it if necessary.
  3. Carefully remove the cooled tube from your experiment assembly and determine the mass of the tube with the metallic copper inside to the nearest 0.01 g.


Chemistry Name

Laboratory Demonstration

Experiment 8 (Reduction of Copper (II) Oxide)

Data and Observations:

Mass of empty test tube / ______grams
Mass of test tube + CuO / ______grams
Mass of test tube + Copper / ______grams

Color of the Copper (II) oxide ______Color of the product left after heating ______

Calculations and Graphs (SHOW WORK)

Original mass of CuO before heating
(Test tube + CuO) – mass of empty test tube / Copper (II) oxide = ______g
Final mass of Copper product
(Test tube + Cu) – mass of empty test tube / Copper = ______g
Mass of Oxygen in original CuO sample
(Mass of CuO) – (Mass of Cu product) / Oxygen = ______g
  1. Calculate the experimental percent composition of copper and oxygen using your data.
  1. Compare your answer from question 2 to the Pre-Lab calculations. Which formula most closely matches your results?


  2. Determine the percent error of your lab data.
  1. Calculate the number of moles of Cu product. (use molar mass and factor-label method)
  1. Calculate the number of moles of Oxygen lost. (use molar mass and factor-label method)
  1. Show the ratio of moles of Copper to moles of Oxygen (Predict the empirical formula)
Moles Cu

Moles O

Conclusion Questions

  1. Identify all the physical properties that confirmed the product was copper metal.
  1. Methane gas was used as a reducing agent in this experiment. The gas was allowed to pass over the CuO inside the test tube as the reactant was heated. How did methane help reduce the CuO to copper metal?
  1. Why was the methane gas ignited at the top of the test tube?
  1. Why was the methane kept burning for 5 minutes after the Bunsen burner was shut off below the test tube?
  1. Would not heating the copper oxide sample long enough make the final ratio of moles of copper to moles of oxygen higher, lower, or have no effect? Explain.
Moles Cu

Moles O

Reduction of Copper (II) Oxide to Copper metal

4 CuO(s) + CH4 (g) ® 4 Cu (s) + CO2 (g) + 2 H2O (g)

Data and Observations:

Mass of empty test tube / ______grams
Mass of test tube + CuO / ______grams
Mass of test tube + Copper / ______grams
Color of the Copper (II) oxide ______

Color of the product left after heating ______