The document describes two methods for forming copper oxide. The first method heats copper powder, allowing it to react with oxygen in the air to form copper oxide. Comparing the masses of copper and copper oxide determines the empirical formula. The second method uses copper(II) sulfate solution reacted with sodium hydroxide to form a copper hydroxide precipitate. Heating this decomposes it into copper oxide and water vapor, allowing calculation of the empirical formula from the known quantities. Procedures are provided for both experiments.

1. Background
An empirical formula describes the simplest ratio for of each type of atom that a compound contains, whereas the molecular
formula gives the actual number of atoms in that compound. The empirical formula of a compound can be derived by finding
the number of moles of the elements in a sample compound and then determining the simplest ratio between them. The
molar ratio represents the simplest ratio for the number of moles of each element in a particular compound rather than the
total number of moles in the compound.
In this lab we will form copper oxide using two methods. The first method is simply to heat dry copper powder until it
combines with oxygen in the air. Comparing the mass of copper to the mass of copper oxide allows us to determine the ratio
of copper to oxygen in the compound.
The second method uses an aqueous solution of copper(II) sulfate (CuSO 4
) combined with sodium hydroxide (NaOH) which
yields a copper hydroxide precipitate. This precipitate is then heated until a decomposition reaction yields water vapor and
copper oxide. Since we know exactly how much copper sulfate we begin with, is possible to calculate the molar quantity of
copper oxide that is formed and then determine its empirical formula.

2. Procedures
Experiment 1
1. Place a clean crucible from the Containers shelf onto the workbench.
2. Place a balance and Bunsen burner from the Instruments shelf onto the workbench.
3. Move the crucible onto the balance and record the mass of the crucible in your notes.
4. Move the crucible onto the workbench and add 10 g of copper (Cu) from the Materials shelf into it.
5. Move crucible onto the balance and record the combined mass of the crucible plus copper in your notes. Does the
number make sense?
6. Move the crucible onto the Bunsen burner. Double-click the crucible to open its properties. Select Show Contents and
click OK. (This cut-away gives you a view of the Crucible's contents.)
7. Turn on the Bunsen burner and set the flame to low. To turn on the burner, click on the black knob. (Clicking multiple
times will increase the intensity of the flame until it is turned off.)
8. Start the Timer by clicking on the clock icon in the lower left of the window frame.
9. The copper will react with the oxygen in the air. You will see the contents of the crucible change color, signifying that the
reaction is complete. Watch the crucible for an additional 30 – 60 seconds to verify that no further reactions occur.
(You may want to use the + or – zoom buttons in the lower right of the screen for a closer view.)
10. Move the crucible onto the workbench to cool and turn off the Bunsen burner.
11. Weigh the crucible and its contents. Record the total mass. (Remember to press Save Notes so you don't lose your
calculations.)
Did the mass of the crucible's contents increase or decrease?
12. Clear the workbench by dragging your containers to the recycling bin beneath the workbench.
Experiment 2
1. Place a 50 mL beaker from the Containers shelf onto the balance. Record the mass.
2. Move the beaker onto the workbench and add 5 g of copper sulfate pentahydrate (CuSO *5H O) from the Materials
shelf.
4 2
3. Weigh the beaker and record the combined mass of the beaker and its contents in your notes.
4. Dissolve the copper sulfate pentahydrate by adding 30 mL of water to the beaker.
Note: In a conventional wet lab, you would remove the container from the balance before you add any chemicals or
solutions. Filling the container separately prevents any spills, sprays, or splashes that might affect your measurements
when they land on the balance.

3. Luckily our virtual labs are spill-, spray-, and splash-free, so we skip that step to save time.
5. Add 10 mL of 6M sodium hydroxide (NaOH) to the beaker. Observe the beaker for signs of a reaction and record your
observations in your Lab Notes.
(You may want to use the + or – zoom buttons in the lower right of the screen for a closer view.)
6. Place a clean beaker from the Containers shelf onto the workbench.
7. Decant the first beaker by moving it onto the empty beaker. Select the Decant option from the pop-up window and click
OK. You should see the liquid transfer to the beaker. The solid will remain behind in the original beaker.
8. Place a clean test tube from the Containers shelf onto the workbench.
9. Determine the mass of the empty test tube by placing it on the balance. Record the mass in your notes.
10. Transfer the solid precipitate from the beaker into the test tube by placing the beaker onto the test tube and selecting
Pour All.
11. Move the test tube on the Bunsen burner and click the black knob to the lowest setting. Start a timer.
12. Over time the solid will decompose into copper oxygen in the air and water is released into the air as water vapor. You
will then see the contents of the test tube change, signifying that the reaction is complete. Watch the crucible for an
additional 30 – 60 seconds to verify that no further reactions occur.
13. Move the test tube on the workbench to cool. (Do not skip this step.)
14. Weigh the test tube and record the mass in your Lab Notes. (Remember to save your notes.)

4. Notes