Lemon “Juice”


“Juice” is a slang term sometimes used for electricity. Batteries are made up of one or more electrochemical cells. Electrochemical cells often consist of two different materials in an electrolytic solution and connected to each other by a wire. In this experiment, you will study some basic principles of electrochemical cells using the juice of a lemon as the electrolyte. You will place small pieces of two different materials into the lemon, and use a voltmeter to measure and display the voltages produced.

OBJECVES

In this experiment, you will

·  build several electrochemical cells and determine which materials make the best electrodes

·  use a volt meter to measure voltages

·  discover which battery combinations produce a bigger voltage

MATERIALS

Digital Multimeter / a car battery
2 alligator clips / graphite pencil (C)
Lemon (or other citrus fruit) / iron nail (Fe)
Various batteries and EMFs / magnesium strip (Mg)
Hand generator / zinc strip (Zn)

Figure 1

PROCEDURE

1. Set the multimeter to DC Voltage and the 200V range.

2. Attach the red Voltage Probe lead and the black probe lead to an alligator clip and do the same with the black probe lead, as shown in Figure 1. You will be attaching the alligator clips to the test materials during this experiment in order to prevent corrosion of the probe leads.

3. Insert a short graphite pencil, sharpened at both ends, into the lemon and an iron nail about ½ inch away. Hook the alligator clip attached to the red test lead to the pencil. Hook the alligator clip attached to the black test lead to the iron nail.

4. Record the voltage reading. Observe whether the voltage reading stays constant, rises, or drops. Record your observations. Note: keep in mind the sign of the voltage sometimes it will read positive and sometimes it will read negative.

5. Switch the positions of the alligator clips. Record the voltage reading and your observations. What happens?

6. Repeat Steps 2-5 for the other electrode combinations listed in the Data Table. Wipe the electrodes with a damp towel and then dry them and return them to the bag.

7. Use the voltmeter to measure the voltage of the following batteries and combinations:
- a D-cell battery
- a car battery
- two 6V lantern batteries (record individual readings as A and B)
- two 6V lantern batteries in series, that is connected pos. to neg. (this is combo #1). You will be touching the volt meter probes to the two open electrodes on the batteries.
- two 6V lantern batteries connected in parallel, that is pos. to pos. and neg. to neg. You will need two alligator clip leads to accomplish this (this is combo #2). You will be touching the volt meter probes to the pos. and neg. electrodes of either battery (check both, are they the same?

8. Use the voltmeter to measure the voltage produced with your hand generator (spin it slowly and consistently until you reach a maximum. Be careful not to over crank the hand generator!). What happens when you turn the crank backward?

DATA

Test Lead
Red Black / Voltage
(V) / Observations / Test Lead
Red Black / Voltage
(V) / Observations
C Fe / Fe C
C Mg / Mg C
C Zn / Zn C
Fe Mg / Mg Fe
Fe Zn / Zn Fe
Mg Zn / Zn Mg
D-cell
Car battery
6V Battery A
6V Battery B
Combo #1 (series)
Combo #2
(parallel)
Test Lead
Red Black / Voltage
(V) / Observations / Test Lead
Red Black / Voltage
(V) / Observations
Hand generator spun CW / Hand Generator spun CCW
Your maximum lemon voltage…

PROCESSING THE DATA

1.  What are the basic parts of an electrochemical cell? Draw one. How does it produce a voltage?

2.  What happens to the voltage reading when you switch the red and black probes?

3.  Which electrode combination gives the highest voltage?

4.  Which electrode combination gives the steadiest voltage?

5.  Which electrode combination would make the best battery? Explain.

6.  The chemical activity of metal is shown by the size of the voltage reading when the metal is paired with carbon in a cell. A high voltage indicates high chemical activity. Rank the three metals (Fe, Mg, and Zn) according to chemical activity, from highest to lowest.

7.  What happened in the series combination of the two lantern batteries? Draw a schematic diagram of this.

8.  What happened in the parallel combination of the two lantern batteries? Draw a schematic diagram of this.

9.  What happens when you turn the hand generator forward? Backward? How does it produce a voltage?

CONCLUSIONS

What did you do? What did you find? What generalizations can you make?

EXTENSIONS

1. Measure the voltage several “lemon cells” connected in series. How high can you get?

2. Try the experiment using other fruits and vegetables.

3. Do the first part of the experiment using other metal electrodes such as aluminum, copper, and lead.