Measurement of Conductivity

The method of obtaining the concentrations of solutions from conductivity measurements is often used industry.

（Examples：HCl, HNO_{3}, _{ }H_{2}SO_{4}, _{ }NaCl, NaOH）

In general, the conductivity of electrolyte solutions peak at high concentrations. Note that this means that a single conductivity value corresponds to two concentration values.

Let A be the substance to be measured. When a solution (of known concentration) of a substance B that reacts with A is gradually added to a solution of A, A and B react, changing the conductivity of the solution. The reaction will saturate at the point where a certain amount of B has been added (the equivalence point), and following this, as B continues to be added, only the additional B will contribute to the change in conductivity. The amount of A can be obtained from the amount of B that is required to reach the equivalence point. This method is called conductivity titration.

Examples:

Hydrochloric acid (HCl) titrated with sodium hydroxide (NaOH):

H+ ＋ Cl^{-} ＋ Na^{+} ＋ OH^{-} → Na^{+} ＋ Cl^{- }＋ H_{2}O

F. W. Fifield and D. Kealey, “Bunsekikagaku I” (Principles and practice of analytical chemistry I), trans. into Japanese, supervised by K. Furuya, Maruzen, 1998, p. 239