A Christmas Lab Your Students Will Actually Like

I'd like to share a fun little lab that I do with my students before finals week. It doesn't require too much prep work and the kids love it. It uses a couple of redox reactions to remove zinc from galvanized flashing and then replace it with copper. We are never far enough in the curriculum to tie it directly to our lessons, but I will refer to it later in the year when we use activity series for single displacement reactions. I hope you enjoy it.

Materials

Galvanized flashing cut into little rectangles (2"x3")

Tin snips

6 M HCl (This is obviously a high concentration and should be treated appropriately) I usually mix 1L and then split into two 600 mL beakers

0.5 M copper (II) nitrate. 500 mL in a 600 mL beaker is usually enough.

Sodium bicarbonate solution in a tub

Masking Tape 1.5"+ in width

Scalpels

Spray Polyurethane

Methods:

1. Have students coat both the front and back of the flashing piece with masking tape. I usually recommend that they leave some extra tape around the edges for handling.

2. Make sure that they press the tape down hard with their fingernail.

3. Students draw a festive shape on one side of the ornament. Larger simple designs generally work better.

4. Cut out the shape with a scalpel and remove the tape. Wherever they remove the tape will be exposed to the acid, the zinc will be removed, and eventually be replaced with dark colored copper metal.

5. After the ornament is prepared, soak the ornament in the beaker of hydrochloric acid. Again, have caution and use tongs when interacting with the acid. Make sure the zinc is submerged.

6. Leave the ornament in the acid until the bubbling stops and the exposed iron is a consistent dark color (usually 5-8 minutes). I often put 8-10 ornaments in one beaker at a time.

7. Remove the ornament and dip it into a saturated sodium bicarbonate solution using tongs. Rinse the ornament well under tap water.

8. Place the ornament in the copper (II) nitrate solution. The students usually like to watch as the copper fills in over the exposed iron. Allow the ornament to soak until the copper is fully coating the iron.

9. Ornaments can be rinsed gently in water. Sometimes I skip the rinse. Set the ornament out to dry. I put out a large piece of butcher paper and allow them to lean them up against the wall.

10. Remind the students to be careful not to bump the copper as its will slough off or leave fingerprints.

11. Once the ornament is dry, have students peel off the tape.

12. Put a light coating of polyurethane on the ornament. Once dry, the copper will be safe to touch.