Figure 1A. A solution of copper(II) sulfate and a piece of zinc metal ready to begin the electron-transfer reaction.
Figure 1B. The reaction has begun. Can you tell that the submerged portion of the zinc metal has become black with a thin coating of finely divided copper?
Figure 1C. A better view of the zinc electrode with a thin film of deposited copper after about one minute of reaction time.
Figure 1D. The same materials after an hour of reaction time. Notice the lighter blue color of the solution (compare to Figure 1B) as most of the copper ion has plated out onto the zinc.
Figure 1E. A better view of the zinc electrode after an hour of reaction time. Note the increased thickness of the loosely adhering copper. The electrode has also become very flimsy due to the reaction of a significant portion of the zinc.
Figure 2A. The Zn/Cu reaction from Figure 1 has been separated into half reactions. The Zn/Zn2+ half reaction is in the beaker on the left and the Cu/Cu2+ half reaction is in the beaker on the right. An ammeter (to measure any current passing in the wire sits in the background. No current is running. The wires have not been hooked up to the electrodes—you can see the alligator clips in the foreground.
Figure 2B. Here the alligator clips have been attached to the electrodes. There is still no current running through the wire (and thus no reaction occurring) because the circuit is not complete without a salt bridge.
Figure 2C. A simple salt bridge of brown paper soaked in saturated NaCl solution is shown with the electrochemical cell in which it will be placed....
Figure 2D. As soon as the salt bridge is in place the ammeter begins to register a current flow in the system. The reaction has begun! Note the deflection of the needle on the ammeter. Unlike in Figure 1, copper will not be deposited on the zinc electrode here. Instead, the zinc electrode will dissolve while the copper electrode will gain mass. The crude salt bridge used here does not support a large current flow; this cell will run slowly.
