Experiment 2.3: Changes in Matter
Student Information
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Purpose
To explore physical and chemical changes in matter.
Materials
Question
What types of clues indicate physical and chemical changes are occurring?
Hypothesis
Write what you predict will happen when you add electricity through a copper wire to a solution of baking soda and water:
Procedure
Step 1: Prepare Solution
Fill the beaker or small glass ¾ full of tap water.
Step 2: Add Baking Soda
Add a teaspoon of baking soda and stir vigorously.
Step 3: Prepare Wires
Use your scissors to strip about ¼ inch of insulation off both ends of each wire. Squeeze the scissors gently as you slowly turn the wire round and round.
Be careful! You can cut yourself if you are not paying proper attention! You will eventually have a cut that goes through the insulation all the way around the wire. At that point, you can simply pull the insulation off.
Step 4: Connect to Battery
Once you have stripped the insulation off both ends of each wire, connect the end of one wire to one of the two terminals on the battery. Do this by laying the wire over the terminal and then pressing it down. Secure it to the terminal with a piece of tape. It need not look pretty, but the bare wire needs to be solidly touching one terminal and not in contact with the other terminal.
Step 5: Connect Second Wire
Repeat step 4 with the other wire and the other battery terminal. Now you have two wires attached to the battery, one at each terminal. Do not allow the bare ends of these wires to touch each other!
Step 6: Immerse Wires
Immerse the wires in the baking soda/water solution that is in the small glass so that the bare end of each wire is completely submerged. It doesn't really matter how much of the insulated portion of the wire is immersed, just make sure that the entire bare end of each wire is fully submerged. Once again, don't allow the ends to touch each other. In the end, your experiment should look something like this:
Circuit diagram showing battery connected to wires immersed in baking soda solution
Step 7: Observe
Look at the bare ends of the wires as they are submerged in the baking soda/water solution. What do you see? Well, if you set everything up right, you should see bubbles coming from both ends. If you don't see bubbles, most likely you do not have good contact between the wires and the battery terminals. Try pressing the ends of the wire hard against the terminals to which they are taped. If you then see bubbles coming from the submerged ends of the wire, then you know that electrical contact is your problem. If not, then your battery might be dead. Try another one.
Step 8: Extended Observation
Once you get things working, spend some time observing what's going on. Notice that bubbles are forming on both wires.
10-Minute Timer for Experiment Duration
Step 9: Check Wire Changes
Allow the experiment to run for about 10 minutes. After that time, pull the wires out of the solution and look at the bare ends. What do you see? Well, one of the wires should not look very different from when you started. It might be darker than it was, but that should be it. What about the end of the other wire? It should now be a different color. What color is it? Write that color down.
Step 10: Solution Color Check
If you let the experiment run for 10 minutes, it's very possible that your solution became slightly colored. Write whether or not that happened and what color, if any, the solution became.
Step 11: Identify Terminal
Looking at the wire that changed color, trace it back to the battery and determine the terminal (positive or negative) to which it is attached.
Step 12: Clean Up
Disconnect the wires from the battery, dump the solution down the sink, run tap water to flush it down the drain, and wash the glass thoroughly. Put everything away.