Decomposition of Copper Carbonate

Introduction

The purpose of decomposing CuCO₃•Cu(OH)₂ is to determine the volume of CO₂ gas that evolves. In this experiment, the water displacement method is used to recover the gas evolved. The volume of CO₂ collected is converted to dry conditions, which is then compared to the theoretical volume calculated.

Go to Top

1. Measure the mass of 0.2 g of CuCO₃•Cu(OH)₂ to the nearest 0.01 gram directly in the test tube.
2. Fill a 25-mL or 50-mL graduated cylinder with water to the top, cover, invert, lower into a filled pneumatic trough, and uncover beneath the water surface.
3. Place the stopper with the delivery tube (plastic tube) into the test tube. Place delivery tube into the inverted graduated cylinder. Heat the copper(II) carbonate slowly and uniformly over a laboratory burner.

   

4. Bubbles will collect in the graduated cylinder. The rate of CO₂ release will begin to slow down when decomposition is near completion. When the bubbling stops, remove the heat and the delivery tube at the same time.
5. Hold the graduated cylinder perpendicular in the water and read the bottom of the meniscus to determine the amount of water displaced by the gas.
6. Record the temperature of the water (which will also be the same temperature of the gas) and obtain the barometric reading.

Go to Top

1. Develop a table to record the various measurements.
2. Write a balanced equation for the decomposition reaction.
3. Determine the number of moles of the mixture used.
4. Determine the theoretical volume of gas produced in the experiment.
5. Determine the actual volume of gas product dry and at STP.
6. Determine the difference between the observed and expected values. Suggest possible reasons for any difference.

Go to Top

Safety

Go to Top

• Have the students construct data tables before trials are run. Two or three trials should be run. Compare data for the entire class. Use a spreadsheet program if one is available.
• The gas delivery tube is constructed from the pulled stem of a Beral pipet. A length of 20-25 cm is sufficient. Push an unpulled end into the hole of a 00 stopper.
• This experiment has proven to be difficult to reproduce. Leakage of the emerging gas seems to be the main problem. Use of sealant materials at the junction between the gas tube and the rubber stopper seems to help.
• Caution students to remove the gas delivery tube from under the water as soon as bubbling stops. (If not, as the gases cool, water may be sucked back into the tube causing it to break.)
• Limewater may be used to confirm that the gas collected is carbon dioxide.
  

Go to Top

• pneumatic trough or large beaker
• test tube (13 x 100 mm)
• 1 hole stopper to fit test tube (00)
• plastic tube (from pulled Beral)
• graduated cylinder (25-mL or 50-mL)
• thermometer
• laboratory burner
• test tube clamp
• CuCO₃•Cu(OH)₂ (solid)
• balance

Go to Top

The original version of this lesson is "Stoichiometry: Mass-Volume" from Laboratory Chemistry, Charles E. Merrill Publishing Co. Modifications were made by:

Sister Noreen Hrnicek
Pius X High School
Lincoln, Nebraska 68510

Kristy Hetzel
West Point High School
West point, Nebraska

Lynne Ruth
Rising City Public School
Rising City, Nebraska

Go to Top