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2 potato clock

Potato clock is an electrochemical cell

Chemical rxn (reaction) occurs in a liquid between two different metals

When a wire is placed to connect the metals, e electrons are pulled from one metal to the other. This is because all metals have a different electronegativity (tendency to pull electrons)

Here we see Cl (chlorine) pulling an electron away from Na (sodium) – we say that Cl is more electronegative than Na.

Elements on the right side tend to pull electrons from elements on the left side:

Look at the period table. We see that some elements are more electronegative (the right side) and some are less so (the left side)

We don’t measure their absolute strength (it would be meaningless to measure billionths of a Newtons of force.) We just compare them on a 4-point scale.

1.0 = very weak electronegativity

4.0 = strongest electronegativity

When e move, we call this motion an electrical current.

* 2 potatos, oranges, grapefruits or lemons

* 2 strips of zinc (or zinc-coated nails)

* 2 strips copper

* insulated wires to connect the strips

Why 2 potatoes? To double the voltage.

The copper strip brings e (electrons) coming from the zinc, to the acid in the potatoes.

1) Electrons leave zinc, when some of the zinc metal turns to zinc ions (Zn 2+).

Sme Zn atoms give e to H+ ions touching the zinc metal. This doesn’t help run the clock.

However, other Zn atoms send e along the wire because they feel the pull coming from the H+ ions in the other potato.

2) H+ ions in contact with copper strip pulls on the e coming from the zinc metal. Hydrogen gas is formed as e electrons combine with H+ ions. Voltage is about 1.1 volts at this point.

3) Zinc metal pushes more e away from itself. The pull at (5) by the H+ ions in the right potato gives a boost of voltage. Voltage is about 2.2 volts. More zinc atoms turn to zinc ions.

4) e  are crowded as they leave (3) enter the negative side of the clock (4)  The excess of electrons makes this wire negatively charged.

5) Too few e–  on the positive (red) wire leaving the clock because e– electrons are grabbed up by the H+ ions in the potato. This makes that wire positive.

Current continues to flow through potatoes and clock – until either all Zn has dissolved, or until the acid in the potatoes is consumed (turned into H2 gas).

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