Conductometric Titration
- Conductivity (κ) depends on the total concentration of ions and their
molar conductivity
- H⁺ has the highest molar conductivity (~350 S cm² mol⁻¹) due to the Grotthuss
mechanism
- OH⁻ is second highest (~198 S cm² mol⁻¹); other ions are much lower (~50–80)
- At the equivalence point, the conductivity profile changes slope — this is
where two best-fit lines intersect
- Unlike pH titrations, conductometric titrations work well for weak acids/bases
and precipitation reactions
Expected Graphs by Reaction Type
- Strong acid + Strong base: V-shape. Conductivity falls sharply (H⁺ replaced by
slower Na⁺), minimum at equivalence, then rises (excess OH⁻)
- Weak acid + Strong base: Slight rise then flat near equivalence (buffering),
steep rise after (excess OH⁻)
- Strong acid + Weak base: Falls steeply (H⁺ consumed), near-flat after
equivalence (weak base excess)
- Precipitation: Falls as ions removed (AgCl↓), flat or slight rise after
equivalence when no more ions precipitate
IB Exam Strategies
- Finding equivalence point: Draw best-fit lines through pre- and
post-equivalence data. The intersection is the equivalence point
- Why conductometric beats pH: No need for indicator, works for weak+weak, works
for precipitation
- NEW 2025: Students must be able to sketch expected conductivity graphs and
identify the equivalence point from data
- Ion mobility order: H⁺ >> OH⁻ >> other ions. Knowing this predicts the shape