Determination of Ionization Constant of a Weak Acid by Potentiometric Titration

Determination of Ionization Constant of a Weak Acid by
Potentiometric Titration
Mendoza, Ronel A.
School of Chemistry and Chemical Engineering
MAPUA Institute of Technology
Abstract
This experiment aims to scrutinize the underlying principles in the determination of ionization
constant of a weak acid by potentiometric titration. Potentiometric titration involves determination of the
potential of a suitable indicator electrode as a function of titrant volume. In the previous experiment, acid-
base titration was performed to determine the concentration of a specific solution. However, there were
moments when an appropriate indicator does not exist. This means that the color of the solution is
obscuring the color change that associates the equivalence point of the solution. A normal mechanical
assembly to perform a manual potentiometric titration includes measuring and recording the cell potential
(in units of millivolts or pH) after every addition of a reagent. This analysis was done by the usage of
digital pH meter for pH measurement as the base titrant is added at different volume intervals. At the end
of the experiment, we were not able to get the pKa of our unknown sample.
Keywords: Potentiometric titration, ionization constant, pH, pKa, weak acid
INTRODUCTION
The objective of the experiment was
for laboratory student to know the
underlying principles of potentiometric
titration. Proper techniques in potentiometric
titration were done to have a good result.
Lastly, this experiment aims to determine
the ionization constant of a weak acid. The
main objective was to determine the identity
of your unknown from the calculated
equivalent weight and estimated pKa.
In a potentiometric titration one
makes a diagram of the volume of titrant
conveyed from a buret against the voltage
(or some capacity straightforwardly
identified with the voltage, for example, pH)
delivered by two electrodes in the solution
being titrated. Provided the equilibrium of
the analytical reaction is favourable what's

more, one picks the right blend of electrodes
there will be a sharp change in voltage at the
equivalence point. This adjustment in
voltage can be utilized as a part of spot of a
color indicator to find the equivalence point.
This is clearly an extremely valuable system
if one is managing a shaded arrangement in
which an indicator would be futile or in a
framework for which a suitable indicator
does not exist. Data obtained by
potentiometric titrations are more reliable
than data gathered from titrations that
involves the usage of chemical indicators
and are specifically very important with
colored or turbid solutions and for the
detection of the presence of unsuspected
species.