Conductometric Titrations: Strong Acid-Base and Weak Acid-Base Titrations

During strong acid-base titration, conductance decreases because fast-moving H3O+ ions are gradually replaced by slower-moving Na+ ions. Although chloride ion concentration remains unchanged, the substitution of highly mobile hydrogen ions with less mobile sodium ions reduces overall electrical conductance until the acid is completely neutralized.

After the equivalence point, adding excess NaOH introduces fast-moving OH− ions into the solution, causing conductance to increase. This post-neutralization increase in conductance creates a distinct linear segment on the conductance versus volume plot, allowing the equivalence point to be identified at the intersection of two straight lines.

HCl neutralizes first because it is a stronger acid than acetic acid. Only after HCl is completely neutralized does the titration of acetic acid begin. The conductance plot shows three linear segments, with distinct endpoints representing the neutralization volumes of each acid.

As acetic acid is titrated, it forms highly ionized sodium acetate, which increases conductance. The acetate ions contribute to electrical conductivity, causing the conductance to rise during this phase. This behavior differs from the initial HCl titration phase, creating a distinct linear segment on the conductance curve.

Conductometric titrations can titrate colored solutions that traditional indicator-based methods cannot analyze. They also work effectively with extremely diluted solutions and weak acids or bases. Additionally, the endpoint is graphically determined, eliminating the need for careful observation near the equivalence point, simplifying the titration process.

The equivalence point is determined graphically by plotting conductance against the volume of titrant added. Two straight lines form on the plot, and their intersection indicates the exact volume of titrant required to neutralize the acid. This graphical method provides a precise endpoint without relying on color indicators.

Conductometric titrations rely on the principle that a solution's electrical conductance depends on the number and mobility of its ions. As ions are replaced during titration, changes in ion concentration and mobility alter the overall conductance, allowing the neutralization process to be tracked and the equivalence point to be identified.