2. Introduction
Conductivity cell
Conductometric titrations
applications
Write a note on conductometric titrations. 5
Write a note on conductometric titrations. 5
Give principle, instrumentation and applications of –
a) Conductometry b) Polarography 10
Draw a labelled diagram of conductometric cell and also
mention their applications 5
Write a note on conductomrtric titrations. 5
Give principle, instrumentation and applications of
a) Conductometric b) Polarography 10
3. Explain the theory of conductometric titrations. How will you
determine end point of various conductometric titrations. 10
What are the advantages offered by conductometric titrations?
5
4. Conductometric titration is an electro- analytical method of
analysis
Used when no suitable color indicators are available for
detection of end point or when the indicator method are not
suitable for analysis.
Conductometric titration is based on measurement of
conductance of ions in a solution.
Reason of Conductance- conductance is due to the migration of
ions. Each cation and anion has different degree of mobility
Conduction involves migration of positively charged ions (H+,
Na+, K+, NH4
+ etc) towards cathode and negatively charged ions
( OH-, Cl-,I-, Br-, CO3
-, SO4
- etc) towards anode.
The movement of ions occurs in such a way that the solution
remains neutral throughout.
End point determination in conductometric titrations -end point
of particular titration is detected by measuring the conductance
of solution which is due to mobility of an ion depends upon
many factors like charge, size, mass and degree of salvation of
an ion.
5. Additional Information
Salvation meaning- In the
process of solvation, ions
are surrounded by a
concentric shell of solvent.
Solvation is the process of
reorganizing solvent and
solute molecules into
solvation complexes.
Solvation involves bond
formation, hydrogen
bonding, and van der
Waals forces.
Solvation of a solute by
water is called hydration.
On anode (+) On cathode (+)
6. Principle of Conductometric Titration
Conductometric titration is based on the measurement of
conductance of the solution.
The conductance of the solution (analyte + titrant) depends on
following three factors –
The number of free ions
The charge on free ions
The mobility of the free ions
During titration one of the ions is replaced by the other and
these two different ions differ in their ionic conductance as well.
So, conductivity of the solution differs during the course of
titration.
A graph is plotted between change in conductance and volume
of titrant added. By this graph an equivalence point can be
detected.
7. Each cation and anion has different degree of mobility
(Conductance).
When a solution of one electrolyte is added (titrant) to a solution
of another electrolyte the overall conductance will depend upon
weather a reaction occur between them or not.
Case-1 - If no chemical reaction occurs then overall conductance
of solution will increases and each ion contribute to conductance
of solution.
Case-2- When a chemical reaction occurs replacement or
substitution of ions takes place which decides that conductance
will either increase or decrease.
Condectometric titration is based on the principle of substitution
of one ions of particular conductance by the ions of different
conductance.
A+B- + C+D- A+D- + C+B-
Standarized
NaOH
Titand- HCl water
NaCl
8. In conductometric titration, tirant (Eg. standardized-NaOH) is
added in small amount and after each addition of titrant,
conductivity of the solution is measured.
Then graph is plotted between amount of titrand eg HCl
added and conductance of solution.
The graph consists of two straight lines intersecting at a
point know as equivalent point (end point)
Amount of titrant-eg NaOH
Titant-
eg
NaOH
Titrand-
eg HCl
Titant Titand
B
C
A
9. Advantages of Conductometric Titration
Conductometric titration techniques are used in various fields
due to their various advantages over other titration techniques.
1. It does not require indicators as titration is based on the
conductance of the solution and endpoint or neutralization
point is determined graphically.
2. It is suitable for colored solutions as well. As the endpoint is
determined graphically,
3. Results are more accurate with minimum error.
4. It is used for the analysis of turbid suspensions, weak acids,
weak bases, a mix of weak and strong acids, etc.
Limitations of Conductometric Titration
With various advantages, conductometric titration has few
limitations as well which are listed below
1. By conductometric titration technique, only a few specific redox
titrations can be carried out.
2. It shows less accurate results when the total electrolytic
concentration is high in solution. It makes it less satisfactory.
3. Not frequently used for Precipitation titration.
10. There are 2 main components for measurement of conductance
of an electrolytic solution, these are
1) conductivity cell
2) Conductometer
The solution whose conductance is to be measured is taken in a
cell known as conductivity cell.
Condectivity cell made up of high quality glass (pyrex), Quartz
and some time fitted with platinum electrodes
The electrodes usually consist of platinum plates sealed into
glass tubes.
Electrodes of conductivity cell are connected to circuit by means
of mercury placed in the tubes.
11. There are TYPE-A conductivity cells,
TYPE-B conductivity cells, and TYPE-
C conductivity cells.
TYPE-A conductivity cells, Having wide
mouth bottle with cork having holes
for passing two platinum wires.
Use- measurement of low conductance
TYPE-B conductivity cells Conductivtity
cell consist of electrodes having
opening for the stirrer and the
burette.
Electrodes are firmly fixed and the
faces of electrodes plates vertical
and parallel.
Use- Measuring the conductance of
precipitation type of reaction
12. TYPE-C conductivity cells Cell consist of wide bore glass tube, the
tip of which has two platinum plates
Contains 2 fixed copper wires, the terminals of which are taken
out for connection.
Platinum plates are coated with platinum black
For determining the cell constant, cell is placed in standard
solution of (KCl) known specific conductance (0.02 or 0.01) at
25oC or 18oC and resistance is measured.
15. The apparatus used for conductance measurement is a form of
wheat stone bridge also known as conductivity bridge.
It made by using wheat stone bridge circuit having 4 arms.
Cell is placed in one arm and resistance constitutes the second
arm.
The other two arms are in the form of calibrated slide wire
resistor.
The detector used may be a galvanometer, or calibrator digital
display.
An Alternating current (AC) of frequency 50-60 Hz is used in
the circuit.
A calibrate switch is there to calibrate the desire value of
conductance.
In order to determine the conductance, the conductivity cell is
dipped into solution and terminals are connected to
conductivity bridge.
The selector switch is set to the proper conductance range and
reading is recorded from galvanometer.
16. Current source :- Alternative current source is used. High
frequency alternating current generator is employed. electrical
potential is applied ions will be transfer and ultimately
conductance take place.
Conductivity meter :- Digital display, calibrator,power switch.
Conductivity cell :- Made of pyrex or quartz and are fitted with
two platinum electrodes. Should be placed in vessel containing
water to maintain constant temp. types of conductivity cells
are TYPE-A, TYPE-B, & TYPE-C.
Electrodes :- Platinum sheets each of 1 cm are fixed at
distance of 1 cm. the surface is coated with platinum black to
avoid polarization effect & increase effective surface area.
platinisation of electrodes is done by coating solutions 3%
chlorplatinic acid & lead acetate on it to gel uniform coating.
electrode usage depends on conductivity & concentration.
17. CONDUCTOMETRIC TITRATION :-
Determination of end point of a titration with the help of
conductivity measurements is termed as conductometric
titrations.
In a conductometric titration the titrant is added.
The values of conductivity are then plotted against the volume
of the titrant in C.C.
Since the measured conductivity is a linear function of the conc.
of ions present two lines will be obtained which will intersect
each other at a point known as “end point” or ”equivalence
point”
18. TYPES OF CONDUCTOMETRIC TITRATION :-
1. Acid base titration
2. Displacement titration
3. Precipitation titration
4. Redox titration
5. Non-aqueous titrations
1.ACID – BASE TITRATION :-
Strong acid- strong base titration :- Fall in conductance due to
replacement of high conductivity hydrogen ions by poor
conductivity of sodium ions.
After equivalence point- Rise in conductance due to increase in
hydroxyl ions.
e.g. HCl vs NaOH
(H++Cl-) + (Na++OH-) (Na++Cl-) + H2O
The strength of HCl can be determined by titrating directly with
NaOH solution.
19. When electrode is measured in a beaker containing HCl (sample
solution) its conductivity is high which is called initial
conductivity.
Because strong acid completely dissociates into H+ ions.
When NaOH is added, OH- of NaOH react With H+ of HCl and
produce water.
Which results in decrease of conductivity on every addition.
At the end - point all the H+ of HCl react with OH- of NaOH
resulting water.
After that point, further addition of NaOH increase conductance
due to OH- which results in ‘V’ shaped graph is obtained
A
B
C
20. Strong acid – weak base titration :- Fall in conductance due to
replacement of hydrogen by ammonium ions. conductance remain
constant due to suppression of NH4OH by NH4Cl
e.g. HCl vs NH4OH
HCl (Strong acid) and NH4OH (Weak base)
Initial conductivity of solution is high due to HCl.
When NH4OH is added, OH- of NH4OH reacts with H+ of HCl and
produce water.
Which results in decrease of conductivity on every addition.
After end point, further addition of NH4OH cause no change in
conductance because NH4OH poorly dissiciates into OH-
HCl + NH4
+OH- NH4
+Cl- + H2O
NH4OH
21. Weak acid – strong base titration:- Initial decrease in conductance
followed by increase due to NaOH.
e.g. CH3OOH VS NaOH
Acetic acid (Weak Acid) and NaOH (strong base)
Initially conductance of solution is low because acetic acid does not
dissociate into H+ ions.
On adition of NaOH, CH3OONa formed and conductivity slightly
increased till the end point.
After end point, further addition of NaOH cause sharp increase in
conductivity due to OH- ions.
CH3OOH + Na+OH- CH3OO-Na+ + H2O
22. Weak acid – weak base titration :- Increase in conductance due to
excess of CH3COOH. Constant conductance due to suppression of
NH4OH by CH3COOH.
e.g. CH3OOH VS NH4OH
Acetic acid (weak acid) NH4OH (weak base).
Initially conductivity is low because acetic acid does not dissociate
into H+ ions.
On addition of NH4OH, ammonium acetate (CH3COO-NH4
+) salt is
formed which has good conductivity increase on every addition of
NH4OH cause no change in conductance and plateau is obtained.
CH3OOH + NH4OH (CH3COO-NH4
+) + H2O
NH4OH
23. 2.Displacement titration
Involve displacement of one ion by another. Displacement
titration type
Titration of salt of strong acid and weak base vs strong bases
Ammonium chloride ( NH4Cl )=salt of strong acid and weak base
while NaOH (Strong base)
Initially cure- plateau- because only displacement of ammonium
(NH4
+) and chloride (Cl-) ions with Sodium (Na+) and Chloride
(Cl-) ions takes place till the end point.
After end point, further addition of NaOH cause sharp increase
in conductivity.
NH4
+Cl - + Na+OH- NH4 OH + NaCl
Titration of salt of strong base and weak acid vs strong acid
Sodium acetate (CH3COONa)= salt of strong base and weak acid)
HCl (Strong acid)
Initially displacement of CH3COO- ions by Cl- ions and
conductivity increased gratually till end point.
24. After end point, the further addition of HCl cause sharp increase
in conductivity.
CH3COONa + HCl CH3COOH + NaCl
Figure: Conductometric titration of a salt of weak acid (sodium acetate) vs.
strong acid (HCl);
Conductometric titration of salt of a weak base (NH4Cl) vs. a strong base
(NaOH)
USE-in determination of alkaloids because alkaloids are weak
bases and insoluble in water
25. 3.Precipitation titration
The precipitation titration does not involve H+ and OH- ions
therefore cannot be carried out much effectively as the acid base
titration.
In precipitation titration one pair of ions gets substituted for
another.
If a cation is to be precipitated, a titrant whose cation has less
mobility is selected for e.g. titration of silver nitrate with KCl.
eg. Ag+ has less mobility.
KCl + AgNO3 KNO3 + AgCl (ppt)
Initially with addition of AgNO3 there is no change in
conductance because Cl- ions are replaced by NO3
- ions and both
have same ionic conductance
But after end point excess of AgNO3 resulted in sharp increase in
conductance.
26. 4.Non aqueous titrations-
Non aqueous titration of weak acid and weak bases can be
preformed .
1. Titration of tetramethyl ammonium hydroxide in methanol-
benzene with weak organic acids in methanol and pyridine
2. Titration of perchloric acid in dioxan-formic acid with weak
bases
27. 5.Redox titration
In redox titrations, there is decrease in conductivity due to
decrease in hydrogen ion concentration at the end point.
Initial conductivity is kept at low level because it is difficult to
detect small change in conductivity due to change in H+ ion
concontration.
Redox titrations mainly performed in acidic medium .
28. Applications of Conductometric Titration
Since conductometric titration is exclusively used in analytical
chemistry, it has various applications. Mentioned below are some
of its major applications:
Conductometric titrations are used to determine water purity. It is
used to check the levels of pollution present in different small
water bodies like lakes, ponds or rivers.
Conductometry can also be used to examine the salinity of
seawater and the alkalinity of freshwater or freshwater bodies.
This type of titration is used significantly in the food industry,
specifically by food microbiologists, to trace various
microorganisms.
Conductometric titration can be used in determining deionized
and distilled water purity or freshness by examining the
equilibrium of chemicals in ionic reactions.
It is also used largely in the pharmaceutical industries to detect
many antibiotics and to check the levels of basicity in various
organic acids.
Used in determination of alkaloids (Weak base) and insoluble in
water
