AP Chemistry 2015-2016
Name:
Determining the Empirical Formula of a Compound
Date:
Per:
Purpose: Due to the fact that copper can form more than one ion, “copper oxide” may refer to one of two
compounds. In this experiment you will convert a sample of a pure copper oxide, to metallic copper, Cu,
by allowing it to react with the gas used to fuel your Bunsen burner. The reaction may be expressed this
way:
Copper Oxide + Propane ➞Copper + Carbon Dioxide + Water
Since all products except the copper escape from the system as gases, the amount of copper produced can
be easily determined. You will use the experimental masses to determine the empirical formula of your
sample of copper oxide.
Prelab:
1. Summarize the purpose statement in 1-2 sentences.
2. Make a detailed flow chart for the procedure below (words, pictures, and arrows).
3. Design an appropriate data table to hold all the data that you will collect for this lab.
4. How will you know when the reaction is complete?
Materials:
2 ring stands
Bunsen burner
Glass elbow
Rubber tube for elbow
Test tube clamp
Thermometer clamp
Test tube tongs
Test tube
Lighter
Test tube rack
Copper oxide sample (one of
two variations)
Electronic balance
125 mL flask
Note: Keep the test tube
Procedure:
horizontal. Gas delivery tube
1. Assemble the equipment needed to conduct this
should not tough test tube.
experiment as shown in the illustration to the right.
2. Determine the mass of a clean, dry test tube to the
nearest 0.01g.
3. Roughly weigh about 2 g of the copper oxide into a
weigh boat.
4. Roll a piece of paper into a tight cylinder and place it in
the previously weighed test tube. Transfer the copper oxide
sample to the bottom of the test tube through the paper
cylinder. Carefully remove the paper cylinder, leaving the
copper oxide confined to the bottom of the test tube.
Determine the mass of the test tube containing the copper
To gas
oxide sample to the nearest 0.01g. Record the mass in your
outlet
data table.
5. Complete the apparatus setup (See picture). Tap the test tube to gently spread the copper oxide into a
layer on the side (bottom) of the test tube.
6. Adjust a slow flow of gas through the glass tube (do not blow the copper oxide around) and with a
lighter 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.
7. Now light and adjust the flame of the Bunsen burner to obtain the hottest possible flame. Heat the
copper oxide by slowly moving the burner flame under the end of the test tube. Continue to heat the
copper oxide until you are certain it is all fully converted to metallic copper. The reaction usually takes at
least five minutes (note: Keep test tube horizontal – gas delivery tube should not touch test tube).
(Procedure continues on back)
8. Carefully heat the wall of the test tube to "chase out" any condensed moisture, which is another
product of the reaction.
9. 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 tube mouth. Extinguish it if
necessary.
10. Carefully remove the cooled test tube from your equipment assembly and determine the mass of the
tube with the metallic copper inside to the nearest 0.01g. Enter the results in your data table.
11. Shake the solid copper plug from the test tube and rub it firmly on a hard surface or hammer it. Can
you observe the characteristic metallic luster of the copper? Is it malleable?
Calculations: Calculate the empirical formula of the copper oxide. Show your work in detail.
Analysis
1. What happened to the oxygen from copper oxide?
2. Write the balanced equation for the reaction of your copper oxide with propane (see purpose section).
Conclusion
Identify any potential sources of error in your experiment. Be specific! You may want to look up what the
different forms of copper oxide look like to determine whether or not you were correct.
Lab report due on Tuesday, September 22