VOLTMETER READING VS TIMEELECTROCHEMICAL SERIESelectronCu depositH₂ bubbleSCHEMATIC MODEL
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KEYS & MODEL
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Left electrode
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Right electrode
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Electrolyte
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Half equations
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MODEL
The voltmeter's red (+) lead is on the right electrode and its black (COM) lead is on the left, so the reading is negative when the left electrode is the positive one.
Starting reading: ideal values from how far apart the two metals are in the electrochemical series. Real simple cells give lower readings.
The more reactive metal is the negative electrode. It gives up electrons, which flow through the wire to the positive electrode.
Direct reaction (schematic): the negative electrode also reacts with the electrolyte by itself. Those electrons never pass through the wire, so the energy is lost as heat, and the reading drifts down. Dashed line on the graph: the reading if there were no direct reaction.
In dilute H₂SO₄, Cu | Ag gives no reaction: neither metal is above H in the electrochemical series, so nothing can take the electrons.
Particle view: SO₄²⁻ ions are not shown.
Bulb brightness is illustrative only: a real simple cell can hardly light a filament bulb.
