[Kelsi Jade]

I'm haveing some trouble with diagraming an electrochemical cell for an orange juice clock. Here is some information about the problem:

The Orange Juice Clock is a galvanic cell made from the combination of a magnesium strip, a copper strip, and juice in a beaker.

The demonstration requires:
-a single AA-cell battery-operated wall clock with a sweep-second hand
-a medium-sized beaker (600 mL is fine)
-enough orange juice or other electrolyte mixture or solution to fill the beaker about 2/3 full (tap water often works fine!)
-a 20-30-cm magnesium strip, coiled at one end or wrapped around a popsicle stick
-a 20-30-cm copper strip, coiled at one end
(Connect the magnesium to the "-" contact of the clock and the copper to the "+" contact).

The problem wants us to draw the electrochemical cell and label the components but I'm unsure how to go about this based on the information above. I know that an EC cell is a connected combination of two half-cells, but I don't see how you can have two 1/2 cells or what would be used as the salt bridge once connected...

Thanks in advance!

[Arkcon]

Yes, the demand for a visible "salt bridge" to separate the two half-cells in these fruit and vegetable "batteries" is a source of confusion.  Here's another one -- a simple length of copper wire, and an unbent paper are pushed into a whole lemon, 1/4" apart, and a charge is felt across the two wires when touched to the tongue"  we've all played with that old trick (at least I hope so, you can try it, if you have the time and materials)"

What happens if the two pieces of metal touch inside the lemon?

What happens if they're set far apart as opposed to 1/4" apart?

Can you guess what the half cell reactions are?

What does a salt bridge really do, and how can a fruit or vegetable do the same thing?

[ARGOS++]

Dear Kelsi Jade;

What you have realised is in real called an “Electrolysis” and not a “Galvanic” or “Electrolytic” Cell.
(As long as the other power overbalance.)

So you have to compare it with the picture in the middle of the page:  "Electrolytic Cell”
        -   and not with both pictures on the begin of the page!
A special application of your Design is finally the “last” picture on the same page.

I hope I have been of some help to you.

Good Luck!
                    ARGOS⁺⁺

[Alpha-Omega]

In 1800 Alessandro Volta made the first battery by layering copper and zinc in a jar of salt water.  The chemical reaction created the first steady supply of electricity. The steady supply of electricity from batteries is used to power all sorts of electrical devices like simple calculators,  clocks, light bulbs, and toys.

Electricity is the flow of electrons. Electron flow can be produced by some chemical reactions:  one between the magnesium strip and the copper strip and the citric acid in the orange juice.

The chemical reaction takes some positively charged magnesium ions leaving behind an excess of negatively charged electrons. The copper strip becomes positively charged by drawing positive ions from the orange juice solution, and then the electrons flow from the negatively charged magnesium to the positively charged copper. This flow of electrons is the electricity produced by the orange juice battery.

That should help you draw the circuit.

This is a good link:

http://imet.csus.edu/imet1/antares/folio/Teaching_Units/echem/echem.htm

I just helped one of my friend’s put 15 of these together for a HS demo at UW.   Look at the electrolytic cell Figure 13..I think that models your project.

[Kelsi Jade]

Can you guess what the half cell reactions are?

What does a salt bridge really do, and how can a fruit or vegetable do the same thing?

Ok, so a salt bridge allows the flow of ions to maitain a balance in charge allowing electrons to continue to flow (e.g. maintaining current?) and the current in the orange juice comes from the e- flow from the metal to the acid?
So there is no "salt bridge" needed as the juice allows the flow to continue itself.

So, in this case would the Mg be oxidized? Which would make it's half-reaction something like:

Mg -> Mg²⁺ + 2e-   

Then what is being reduced?

[Kelsi Jade]

The copper can't be reduced because there is no copper ions in the orange juice origionally right?

[Alpha-Omega]

Can you tell me your exact setup?  From what I anm reading in your description you do not have a salt bridge.  If you give me a very good description I can give you a very good answer,

The materials in the system you are using can be arranged in a number of various configurations to demonstrate various systems/principles.


You listed the following materials:

The demonstration requires:
-a single AA-cell battery-operated wall clock with a sweep-second hand
-a medium-sized beaker (600 mL is fine)
-enough orange juice or other electrolyte mixture or solution to fill the beaker about 2/3 full (tap water often works fine!)
-a 20-30-cm magnesium strip, coiled at one end or wrapped around a popsicle stick
-a 20-30-cm copper strip, coiled at one end
(Connect the magnesium to the "-" contact of the clock and the copper to the "+" contact).

The way you have listed them...this appears to be an electrolytic cell.  Here, that link I sent you....

http://imet.csus.edu/imet1/antares/folio/Teaching_Units/echem/echem.htm

Can you point to your configuration?