Overview: In this exploration you will be observing reactions of a copper compound and aluminum. Copper and Aluminum are common substances. Copper has a distinctive appearance when it is an ion and when it is an element. Elemental aluminum’s appearance is more typical of metals. In the course of this exploration the appearances of these substances will change. As we discussed in class when the appearance of something changes or if a new substance appears and another disappears a chemical reaction has taken place. By the end of this experiment you will observe some chemistry “magic.” The "magic" lies in the transformation of ions into atoms and atoms into ions.
Equipment: Crucible, iron ring, clay triangle, ring stand, crucible tongs, 50-mL beaker, stirring rod, bunsen burner, burner lighter
Chemicals: distilled water, CuCl2-2H2O hydrate crystals, 12-cm aluminum wire (A “hydrate” is an ionic compound that has water molecules incorporated into its crystal structure, yet it doesn’t appear wet.)
Procedure A:
1. Weigh a dry crucible. Mass: ________________
2. Obtain about 1 gram of the CuCl2-2H2O crystals from the stock bottle and place this into the crucible.
3. Weigh the crucible with the crystals. Mass _____________. Observe and record the appearance of the crystals.
4. Gently heat the bottom of the crucible with a small blue flame moving the burner around with your hand holding the base. You want to heat the crystals evenly in the crucible, but not too strongly.
5. Observe and record any change in the appearance of the crystals.
6. Keep heating the crucible until the change appears complete. CAUTION: When the change is almost complete the crystals can pop. Heat carefully to minimize the loss of any crystals.
7. When the change is complete turn off the bunsen burner and allow the crucible to cool for 5 minutes carefully lift the crucible with the tongs and weigh it. Mass:_____________.
8. Continue to allow the crucible to cool until you can touch it. Transfer the crystals from the crucible to an empty 50-mL beaker with the stirring rod. Add small amounts of water to the crucible to rinse out the remaining crystals and add these rinsings to the 50-mL beaker. Use a maximum of 10 mL of distilled water.
9. Record your observations of when the water is added.
Procedure B:
Thoroughly dissolve the crystals in the water by stirring. Observe and record any changes noticed.
Take the aluminum wire and coil it into a flat spiral that will fit into the bottom of the 50-mL beaker and be completely immersed in the solution.
Place the coiled wire into the beaker and observe and record any changes. Keep an eye on this solution and the wire over the next several minutes noting any changes that are slower than those, which were immediate.
Cover the beaker with parafilm. Write your initials in pencil on the white label space on the beaker. Store this beaker in your lab cabinet at the back of the bottom shelf
Check your beaker the next day. Record your observations.
Procedure C:
Remove as much of the deposit from the Aluminum wire as possible with your stirring rod. Add several drops of 1 M HCl and stir.
For a piece of filter paper into quarters. Place the folded paper into a funnel. Open the filter paper and filter the deposit out from the solution. Discard any of the wire that remains.
Rinse the solid with distilled water. You can pour the filtrate (liquid) into the sink.
Remove the filter paper and carefully set it on a piece of paper towel.
Burnish your brown powder by gently rubbing a stirring rod on it to flatten it. Notice the change in appearance.
Discard these components in the trash when you have completed your observations.
Questions:
Procedure A:
1. What happened to the mass of the CuCl2 after it was heated? To what do you attribute the change in mass?
2. What substance must be present to give CuCl2 its distinct color?
Procedure B:
1. What is the characteristic color of copper chloride in the solution? What happens to the color of the solution after the aluminum wire is put in?
2. What is the initial appearance of the aluminum wire surface? How does the aluminum wire look after the reaction?
3. How do you account for the change in the aluminum wire?
4. Where did the residue come from?
Procedure C:
Overall:
1. Give the electron configurations of Cu2+ and Cu.
2. Give the electron configurations of Al and its ion.
3. Explain in sentences the reaction that took place in terms of the forming of ions from atoms and atoms from ions. Then use this reaction to explain with sentences the macroscopic changes you observed.
