QS Study

Conductometric Titration of weak acid and strong base:

Conductance of electrolytes depends on the number of ions and their speeds. For conductometric titration experiments a known volume of the solution to be titrated is placed in a beaker and a conductivity cell dipped into it. The conductivity cell is now connected to one end of the Wheatstone’s bridge.

Let us consider that ethanoic acid is titrated against NaOH. The initial conductance of the acid solution is very low because of low ionization of the weak acid. However, as NaOH is gradually added to the acid solution a salt, CH3COONa, will be formed which ionizes readily to form Na+ and CH3COO ions. The ethanoate ions at first tend to suppress further ionization of the acid due to common ion effect. But after a while the conductance of the system increases because the conducting power of the completely ionized salt exceeds that of the weak acid. This continues to increase up to the end point, V [Figure]. Beyond this point as more NaOH is added the conductance rapidly increases due to highly conducting OH. Consequently, the linear portion of the conductance curve in the alkaline region is steeper. The end point is the point of intersection of the two lines – one in the acidic region and the other in the alkaline region.