Potentiometric and Conductometric Titrations: Choosing the Right Method
Two ways to locate an equivalence point without a colour-change indicator — and why one suits coloured or turbid solutions better than the other.
Potentiometric titration: tracking potential
An indicator electrode — a glass electrode for acid-base titrations, a platinum electrode for redox titrations — is paired with a reference electrode, and the measured potential is plotted against titrant volume added. The equivalence point is the inflection point of this curve, where the slope is steepest, and it can be located more precisely using a first-derivative plot (dE/dV peaks sharply at equivalence) or a second-derivative plot (d²E/dV² crosses zero at equivalence).
Conductometric titration: tracking conductance
Conductance changes as ions are consumed, produced or replaced during a titration, and the titration curve is usually two intersecting straight-line segments rather than a smooth curve — the equivalence point is their intersection. For a strong acid titrated with a strong base, conductance starts high (because H⁺ has very high ionic mobility), falls as H⁺ is replaced by a less mobile cation, reaches a minimum near equivalence, then rises again past equivalence as excess titrant ions accumulate.
Choosing between the two methods
| Situation | Better-suited method |
|---|---|
| Coloured or turbid solution, where an indicator colour change is hard to see | Either method avoids a visual indicator; conductometric is particularly robust since it does not depend on an electrode responding to one specific species |
| Very dilute solutions | Potentiometric, generally more sensitive at low concentration |
| Weak acid–weak base, where indicator choice is genuinely difficult | Potentiometric, using the derivative-plot inflection point |
| Precipitation or complexometric titrations with a suitable ion-selective electrode | Potentiometric |
Where this fits a prep plan
Both methods sit within the analytical chemistry portion of CSIR-NET Part C and GATE Chemistry (CY), usually alongside the titration-indicator basics and conductance theory covered elsewhere.
FAQs
How is the equivalence point found precisely in a potentiometric titration?
Using a first- or second-derivative plot of potential against titrant volume, rather than reading the inflection point directly off the raw curve by eye.
Why does conductometric titration give straight lines instead of a smooth curve?
Because conductance changes roughly linearly with the concentration of each dominant ionic species between the points where the reaction’s stoichiometry changes, producing distinct linear segments.
Which method appears more often in GATE and CSIR-NET numerical problems?
Both appear. Potentiometric questions more often involve derivative-based equivalence-point calculations; conductometric questions more often involve reading or sketching the straight-line intersection graph.
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