Potentiometry, Ion-Selective Electrodes and Voltammetry
An electrode can be a sensor as well as a site of reaction. Measuring its potential at near zero current reports concentration, while sweeping the potential and recording current reports both what is present and how it reacts.
What a learner can do afterwards
- Explains how a glass electrode develops a potential that tracks pH and why a reference electrode is needed
- Calibrates an ion-selective electrode and applies a selectivity coefficient to assess an interference
- Reads a cyclic voltammogram and identifies a reversible couple from peak separation and peak ratio
- Explains why stripping methods reach such low detection limits
1 · Read
You have seen how a standard potential predicts a cell voltage and how concentration shifts it, yet one electrode potential can never be measured alone. Only a difference between two electrodes can be read, so every measurement pairs your electrode with a reference whose potential stays fixed. Each half reaction carries a standard reduction potential against a hydrogen reference set at zero volts. The cell voltage is the cathode value minus the anode value, and a positive result means the reaction runs on its own.
A pH meter shows the idea in action. A glass electrode builds a potential that tracks pH, the meter reads its difference against the reference, and the Nernst link turns that voltage into a pH value. An ion-selective electrode works the same way: calibrate it, read the voltage, and convert to concentration. A selectivity coefficient then says how much a second ion would disturb that reading, so you can judge whether an interference matters.
Sweep the potential and record the current, and you learn both what is present and how it reacts. A reversible couple draws a matching pair of peaks with steady spacing and near-equal heights. Unequal peaks warn that the oxidised form changed after the sweep, so the return wave shrinks. Stripping methods go further down: they gather the target onto the electrode before measuring, which is why even tiny traces stand out.
Hold the potential steady to read concentration; sweep it to read behaviour.
2 · Watch
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Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.