PHARMACEUTICAL ANALYSIS-I
ELECTROCHEMICAL METHODS OF ANALYSIS
CONDUCTOMETRY
1
ELECTROCHEMICAL METHODS OF ANALYSIS
• CONDUCTOMETRY
• INTRODUCTION
Conductometry is an electrochemical method of analysis which is concerned with electrical
conductance
• through an electrolyte solution.
It is defined as determination or measurement of the electrical conduction of an aqueous electrolyte
solution by means of a conductometer. The electrical conductivity or conduction of an electrolyte
solution depends on:
Type of ions (cations, anions, single charged, double charged).
Concentration of the ions.
Temperature.
Mobility of ions (Its velocity-speed or rate of movement) through the solution. It is influenced by
-08-2020 factors such as mass, charge, size And extent of solvation of electrolyte. 2
CONDUCTOMETRY
PRINCIPLE
The principle involved in conductometry is based on the conductance of electrical current by aqueous
electrolyte solutions in a manner similar to that of metallic conductors.
The electrical conduction is in accordance with the Ohm’s law which states that the strength of current
(i) passing through a current conductor is directly proportional to the potential difference (V) applied
across the electrodes, and inversely proportional to the resistance offered by the conductor.
V
i.e., i = ---------
R
Where,
i = Current in amperes
V = Potential difference in volts
R = Resistance in Ohms
08-04-2021 3
CONDUCTOMETRY
CONDUCTIVITY CELL
The cell which is used to measure the conductivity of a solution is called as conductivity cell.
Conductivity cells are made up of pyrex or quartz and are fitted with two platinum electrodes.
These cells should be placed in a large vessel containing water in order to maintain constant
temperature.
08-04-2021 4
CONDUCTOMETRY
CONDUCTOMETRIC TITRATIONS
Principle: The determination of end point of a titration by means of conductivity measurements is
known as conductometric titration.
During the course of titration, the conductivity of the solution changes, since there is change in the
number and mobility of ions.
At the end point of the titration, there is a sharp change in the conductivity of a solution shown by the
intersection of the lines in the graph of conductivity Vs volume of titrant added.
08-04-2021 5
CONDUCTOMETRY
CONDUCTOMETRIC TITRATIONS
1) CONDUCTOMETRIC TITRATION OF STRONG ACID AGAINST STRONG BASE
Reaction: HCl + NaOH NaCl + H2O
When HCl is taken in a beaker as titrate, the initial conductivity is high, because strong acid completely
dissociates into H+ ions and the ionic conductivity of H+ is 350. When NaOH is added as titrant from burette, the
OH- and H+ reacts to produce water and the number of H+ ions decreases and the conductivity gradually
decreases after every addition of NaOH. After the end point, when all the H+ has reacted, the addition of NaOH
causes increase in the number of OH- and hence the conductivity starts to increase (ionic conductivity of OH- is
199).
08-04-2021 6
CONDUCTOMETRY
CONDUCTOMETRIC TITRATIONS
1) CONDUCTOMETRIC TITRATION OF STRONG ACID AGAINST STRONG BASE
Reaction: HCl + NaOH NaCl + H2O
A plot of conductivity Vs volume of NaOH added shows a V shaped curve as shown in figure. The first part of
the curve shows steep fall in conductivity because of decrease in H+ (ionic conductivity - 350) and second part
of the curve shows gradual increase because of increase in OH- (ionic conductivity - 199).
08-04-2021 7
CONDUCTOMETRY
2) CONDUCTOMETRIC TITRATION OF STRONG ACID AGAINST WEAK BASE:
Reaction: HCl + NH4OH NH4Cl + H2O
Strong acid (HCl) is taken in conductometric quartz vessel and weak base (NH4OH) is added slowly as a
titrant in the HCl analyte solution. Initially concentration of H+ ions is more and solution of HCl shows higher
conductance. After addition of NH4OH, hydrogen ions reacts with hydroxide ions of NH4OH and conductance
of the solution decreases. At the equivalence point, conductance of the solution is lowest because all the H+
ions reacts with hydroxide ions .
After the equivalence point, addition of NH4OH not affect the conductance and remain constant due to
common ion effect between NH4OH and NH4Cl.
08-04-2021 8
CONDUCTOMETRY
08-04-2021 9
CONDUCTOMETRY
08-04-2021 10
CONDUCTOMETRY
• APPLICATIONS OF CONDUCTOMETRY
Conductometric titrations are used to check the water pollution in river and
lakes.
It is used to determine the alkalinity of fresh water.
It is used to determine the salinity (saltiness) of sea water in oceanography.
Deuterium oxide (D2O) content in water- Deuterium mixture is determined
by Conductometry titration.
• It is used in food microbiology for tracing microorganisms.
It is used to estimate ash content in sugar juices.
Quantitative analysis of substances like acids, bases and electrolytes can be
performed by
• conductometry up to a concentration of 10% by weight.
The purity of distilled and deionized water can be determined.
Ionic product of water ( conc. Of H+ and OH- ions) can be determined.
08-04-2021 11
THANK YOU
-08-2020
12
