The principle on conductometric titration is based in the fact that during the titration, one of the ions is replaced by the other and invariably thses two ions differ in the ionic conductivity with the result that the conductivity of the solution varies during the course of the titration.Take,for example,the titration between strong acid, say HCl. and a strong base, say NaOH.Before NaOH is added the conuctance of HCl solution has a high value due ti the persence if highly hydrogen ions.As NaOH is added,`H^(+)` ions are the replaced by relatively slower moving `Na^(+)` ions.Consequently, the conductance of the solution decrease and this continues right upto the enuivalence point where the solution contains only NaCL.Beyond the equivalence point if more of NaOH is added, then the solution contains an excess of the fast moving `OH^(-)` with the result that its as more of NaoH added, we plot the conductance value vs the amount of NaOH added we get curve of the type shown in figure.The descending portion AB represents the conductance before the equivalence point (solution cintains a mixture if acid HCl and the salt NaCL and the ascending portion CD represents the conductances after the equivalence point (solution contains the salt NaCL and the excess of NaOH). The point E which repersents only the minimum conductance is alkali and thus repersents the equivalence point.This point can, however, be obtained by the extrapoltion of the lines AB and CD and therefore one is not very particular in location this point experimentally as it is in the case of ordinary acid -base involving the acid base indicators
LET us take the specific exaanple of acetic acid being titration against NaOH.Before the addition the of alkali, the solution shows poor conductance due to feeble inization of acetic acid.Initially the addtion of alkali causes not only the replacement of `H^(+)` by `Na^(+)` but also suppresses the thus the conductance of the solution decrease in the begnning .But very soon the conductance starts increasing as addetion NaOH thus causing neutralizes the undissociated HAc to HAc with strong condutance eletroyte `Na^(+)Ac^(-)`.The increase in conducting `OH^(-)` ions gtthe graph near the highly equivalence point actual equivalence point can as usual be ontained by the extrapoiation method
In all thses graphs it been assumed that the vloume change due addition of solution from burette in negligible heane vloume change of the sloution in beaker the conuctance of which is measured is almost constant throughout the measurement
The most appropriate titration curve ibtained when a mixture of a strong acid (say HCl) and a weak acid (say`CH_(3)`COOH0 is titration with (say NaOH) will be
A.
B.
C.
D.
