When soldering, place the penny on a ceramic fiber square, with the end of a copper wire overlapping the penny 2-3 mm. Ask a partner to apply pressure to the wire to hold it in place while you are soldering the joint -use a rubber stopper as before to do this.
Four arrangements of copper pennies in the golden penny experiment.
The bottom of the beaker is half-covered with 30-mesh zinc metal. (A) Two pennies are lying on top of the 30-mesh zinc.
(B) Two pennies are lying on the bottom of the beaker but not in contact with the 30-mesh zinc. (C) A penny soldered to copper wire is immersed in solution, the other end of the copper wire being soldered to a strip of zinc metal in contact with 30-mesh zinc on the bottom of the beaker. (D) A penny soldered to copper wire is immersed in solution. The solution in the beaker is 1 M NaOH.
Review the General Soldering Instructions in Part I. Place the freshly tinned tip of the penny next to the wire angling the iron to get good thermal contact. Don't dab at the joint with the tip of the iron while soldering.
When the solution has warmed, use forceps to place two copper pennies on top of the granular zinc metal and two pennies in the area that is free of granular zinc (make sure that the pennies on the uncovered side do not contact even one grain of zinc). Bend a small "foot" on the penny in the beaker as shown in Figure 5. The "foot" of the zinc strip should rest on the granular size so that both are in direct contact. The penny should be completely immersed in solution but should not contact any granular zinc metal on the bottom of the beaker. Finally, hang the last penny (the one with only copper wire soldered to it) over the edge of the beaker so that the penny is completely immersed in solution. See Figure 5. HINT- use an empty 400-mL beaker to bend and shape your soldered metal pieces to match what is pictured in Figure 5. Do this before attempting to put them in the 400-mL beaker containing your warm NaOH solution. 30min.
Leave the pennies in the beaker until some of them turn a silvery color. This may take anywhere from 5 to 30 min., depending on the temperature of the solution. (Some of the pennies will never turn silver even after waiting an hour or more.)
Which pennies turn a silvery color? Is it the three pennies that are in contact with the solution and with zinc, either directly or through the copper wire? Or is it the three pennies in contact with the solution but not indirect or indirect contact with zinc metal? 5-10min.
Using a pair of forceps, remove the pennies that have turned a uniform silvery color, rinse them with water, and put the pennies on a hot plate for a few seconds. Watch what happens to the silver-colored pennies as they heat on the hot plate. Keep the solution warm in the beaker in case you need to repeat some part of the experiment or try some new experiment, as described below. 5-10min.
Further Experiments. Solder another length of copper wire to a shiny clean penny. Actually, you can use the lone penny soldered to the copper wire from the first part of the experiment, just clean it with steel wool and deionized water. Connect one lead of a voltmeter to a zinc strip and the other lead to the copper wire soldered to the penny. Using the same solution you prepared earlier, immerse the zinc strip and penny in the solution. Is there a voltage difference between the zinc strip and the copper wire soldered to the copper penny? Which metal is the electron source (the negative terminal of this electrochemical cell)? 5-10min.
Do you think a current flows in the copper wire connecting the zinc strip and copper penny when both are immersed in the solution? If so, which direction will electrons flow, and what are the anode and cathode reactions? Put the digital voltmeter into its current measuring mode on its most sensitive (microampere) scale. Then see if any current is flowing when you connect the meter in series between the copper wire soldered to the penny and to the zinc strip -both the penny and the zinc strip should be immersed in the hot 1 M NaOH solution. The series connections should look like this: Penny/copper wire/(+) ammeter(-)/zinc strip. How large a current flows? . Is the current (charge flow) from penny to zinc strip or vice versa?
In wires the charge carriers are electrons. Current (defined as a flow of positive charge) is opposite to the flow of electrons. In which direction are electrons flowing: from penny to zinc strip or vice versa?
