Chemistry · Chapter 17

The Potential Ladder

Eighteen real half-cells, drawn at their true heights on one voltage scale. Pick any two and the gap between the rungs is the standard cell potential. The higher rung is always the cathode.

The ladder drawn to scale

A scaled ladder of standard reduction potentials with your two picks marked

The arithmetic

Cathode minus anode, with the free energy and K that follow
1.10volts spontaneous
Cathode, the higher rung: Cu2+ / Cu at +0.34 V
Anode, the lower rung: Zn2+ / Zn at −0.76 V
Electrons moved, n: 2
What happens: zinc hands electrons to copper ions

Choose two rungs

Tap a couple to drop it into the active pick

How to read it

Every value on the ladder is written as a reduction, so you never flip a sign. You subtract. Take the cathode value and take away the anode value, and the answer is the voltage you would measure.

Anything high on the ladder is a strong oxidizing agent, because it wants electrons badly. Anything low is a strong reducing agent, because it parts with them easily. So a species can oxidize anything that sits below it.