Conductometric Titrations

Conductometry is a measurement of electrolytic conductivity to monitor a progress of
chemical reaction. Conductometry has notable application in analytical chemistry, where
conductometric titration is a standard technique.
conductometric titration: In this method we determine the point where reaction is
completed wi t h th e he l p of a con du c t ome t e r th a t me a s u r e s t h e changes in
conductance of solution produced by the ions in the solution.This point at which this transition
occurs is called Equivalence point.
At Equivalence point we measure the volume of base used to neutralize the acid ions completely
in the solution. Putting these values in formula we can get the strength of acid
The principle of conductometric titration is based on the fact that during the titration,one of the
ions is replaced by the other and invariably these two ions differ in the ionic conductivity with the
result that conductivity of the solution varies during the course of titration. The equivalence point
may be located graphically by plotting the change in conductance as a function of the volume of
titrant added.
1-Strong Acid with a Strong Base, e.g. HCl with NaOH:
HCl + NaOH? NaCl + H2O
H+ + Cl- + Na+ + OH-? Na+ + Cl- + H2O
Before titration the conductance is high which is due to HCl ? H+ + Cl-mobility of H+ is 350
and that of Cl- ion is 73. Upon addition of NaOH the H+ ion reacts with OH- ion to form the
very weakly ionized water molecule. This means that the H+ ion is removed from the medium
and replaced by Na+ ion which has a mobility of 43; thus a continuous abrupt decrease in
conductance occurs during the titration till the end point. Beyond the end point there is excess
Na+ and OH- ions with 43 and 198 mobility due to continuous addition of NaOH So there is
continuous increase in conductance and the curve will have a V shape , the end point is the
minimum of the curve.