A chapter of Advanced Pharmaceutical Analysis

1. Conductometry
Nuzhat Tasnim Amin
Lecturer
Dept. of Pharmacy
Varendra University

2. Definition
• Conductometry is the measurement of the electrical conductivity, of an
electrolyte solution, during the course of a chemical reaction, and the
determination of the quantity, of a material present in the solution, by
the measurement of its effect on the electrical conductivity of the
mixture/solution.

3. Electrolyte
• When ions are present in water, the water is able to conduct electricity.
The solution is known as an electrolyte.
• An electrolyte is a substance that contains free ions and behaves as an
electrically conductive medium.
• A strong electrolyte is one where many ions are present in the
solution and a weak electrolyte is one where few ions are present.
Strong electrolytes are good conductors of electricity and weak
electrolytes are weak conductors of electricity.
• Non-electrolytes do not conduct electricity at all.

4. Conductivity
• Conductivity of an electrolyte solution is a measure of its ability to conduct
electricity.
• Conductivity, in general, is the capacity to transmit something, such as electricity
or heat.

5. Mobility and Conductivity
• Mobility is the speed with which a particle moves. It depends upon
the applied electric field.
• Electrical mobility is the ability of charged particles (such as
electrons or protons) to move through a medium in response to
an electric field.
• Conductivity of a substance is defined as 'the ability or power to
conduct or transmit heat, electricity.
• Conductivity is proportional to the mobility.

6. Principle
• During a conductometric titration process, one ion is replaced with
another and the difference in the ionic conductivities of these ions
directly impacts the overall electrolytic conductivity of the solution.
• The addition of an electrolyte to a solution of another electrolyte, it will affect the
conductance of the solution.
• If ionic reaction occurs the conductance may either increase or decrease.
• Thus in the addition of a base to a strong acid, the conductance decrease due to
replacement of H+ ion of high conductivity by another cation of lower conductivity.
• For example, the ionic conductivity of an H+ ion is greater than that of a Na+ ion.
This is because an ion’s conductivity depends on its mobility. Since the H+ ion is
much smaller than the Na+ ion, it moves through the ionic solution faster.

7. Theory
• The theory behind this type of titration states that the end-point
corresponding to the titration process can be determined by means of
conductivity measurement.
• For a neutralization reaction between an acid and a base, the addition of the
base would lower conductivity of the solution initially. This is because the
H+ ions would be replaced by the cationic part of the base.
• After the equivalence point is reached, the concentration of the ionic entities
will increase. This, in turn, increases the conductance of the solution.
• Therefore, two straight lines with opposite slopes will be obtained when the
conductance values are plotted graphically. The point where these two lines
intersect is the equivalence point.

8. Process
For the conductometric titration of an acid with a base, the general process is
as follows:
 10 ml of the acid must be diluted with approximately 100 ml of distilled
water.
 A burette must now be filled with the base and the initial volume must be
noted.
 In this step, a conductivity cell must be inserted into the diluted acid
solution in a way to be completely immersed.
 Now, the conductivity cell can be connected to a digital conductometer in
order to obtain an initial reading.

9. Process
 The base must now be added dropwise into the acid solution. The volume of base
added must be noted along with the corresponding change in the conductance.
 A sharp increase in the conductance of the solution implies that the endpoint has
been reached. However, a few more readings must be taken after the endpoint of
the titration.
 These observed values must now be plotted graphically. The equivalence point
can be obtained from the point of intersection between the two lines.

10. Advantages
 This process is very useful in the titrations of very dilute solutions and weak
acids.
 The end-point of this method of titration is very sharp and accurate when
compared to a few other titration processes.
 This type of titration is applicable for solutions that are colored or turbid,
and for which the endpoint of the titration with normal indicators cannot be
observed easily by the human eye.
 Conductometric titration has numerous applications in acid-base
titrations, redox titrations, precipitation titrations, and complex titrations.

11. Disadvantages
1. Only a few specific redox titrations can be done with the help of this
process. This is because the conductivity of the solution is masked by
relatively high hydronium ion concentration.
2. In certain cases, the accuracy of conductometric titration is low when
the concentrations of the electrolyte are high, making the titration
process unsatisfactory.

12. Applications
• The estimation of the purity of distilled water or deionize
water.
• To measure the salinity of sea water.
• To detect ions after separation by an ion chromatographic
technique.
• For determining the concentration of substances in solution
containing electrolyte.
• For determining critical micelle concentration.
{The critical micelle concentration (CMC) is defined as the concentration of surfactants above which micelles form.}

13. Strong acid v/s strong base
• In the conical flask HCL (strong acid) is taken as an analyte.
• In the burette NaOH (strong base) is taken as titrant.
• HCl is a strong acid so, it dissociates very rapidly. HCl gives H+ and Cl- ions. The
mobility of H+ ion is very high, and it’s conductance is also very high. So, at the
starting stage of titration, the initial conductance is very high.
• NaOH is a strong base so, it dissociates very rapidly. NaOH gives Na+ and OH-
ions.
• H+ ions and OH- will react and a neutralization reaction will take place, which will
form H2O.

14. Strong acid v/s strong base
• At first HCl will be present in the conical flask, and the conductometer will trace its
conductance, which was very high. NaOH is taken in the burette and added drop by drop.
Neutralization reaction will take place by replacing the H+ ions with OH- ions and water
started to form. As the concentration of H+ ions decreases, the conductance also decrease.
After the completion of neutralization reaction, there will be no HCl left. Then further
addition of base from the burette, will increase the concentration of OH- ions in the solution,
which will again increase the conductance. The point at which sudden rise of conductance
occurs, is called the end point/equivalent point. By plotting the change in conductance
against the volume of base added we will get a curve of two opposite straight lines.

15. Strong acid v/s weak base
• In the conical flask H2SO4 (strong acid) is taken as an analyte.
• In the burette NH4OH (weak base) is taken as titrant.
• H2SO4 is a strong acid so, it dissociates very rapidly. H2SO4 gives H+ and
SO4
2- ions. The mobility of H+ ion is very high, and it’s conductance is also
very high. So, at the starting stage of titration, the initial conductance is very
high.
• NH4OH is a weak base so, it dissociates very slowly. It gives NH4
+ and OH-
ions.
• H+ ions and OH- will react and a neutralization reaction will take place,
which will form H2O.

16. Strong acid v/s weak base
• At first H2SO4 will be present in the conical flask, and the conductometer will trace its conductance,
which was very high. NH4OH is taken in the burette and added drop by drop. Neutralization reaction will
take place by replacing the H+ ions with OH- ions and water started to form. As the concentration of H+
ions decreases, the conductance also decrease. After the compellation of neutralization reaction, there will
be no H2SO4 left. Then further addition of base from the burette, will increase the concentration of OH-
ions in the solution. But it will also start the formation of (NH4)2SO4. Among ammonium sulphate and
ammonium hydroxide, ammonium ion is common, which will introduce the common ion effect. As a
result, the conductance will remain constant. The point at which conductance starts to show a horizontal
line, is called the end point/equivalent point. By plotting the change in conductance against the volume
of base added we will get a curve of two straight lines.

17. Weak acid v/s strong base
• In the conical flask CH3COOH (weak acid) is taken as an analyte.
• In the burette NaOH (strong base) is taken as titrant.
• CH3COOH is a weak acid so, it dissociates very slowly. It gives H+ and CH3COO-
ions. As the analyte dissociates first, instead of having high conductance of H+ ion,
at the starting stage of titration, the initial conductance is very low.
• NaOH is a strong base so, it dissociates very rapidly. NaOH gives Na+ and OH-
ions.
• H+ ions and OH- will react and a neutralization reaction will take place, which will
form H2O.

18. Weak acid v/s strong base
• At first CH3COOH will be present in the conical flask, and the conductometer will trace its
conductance, which was very low. NaOH is taken in the burette and added drop by drop.
Neutralization reaction will take place by replacing the H+ ions with OH- ions and water started to
form. As the concentration of H+ ions decreases, the conductance also decrease. After the
compellation of neutralization reaction, there will be no CH3COOH left. Then further addition of
base from the burette, will increase the concentration of OH- ions in the solution, which will again
increase the conductance. The point at which sudden rise of conductance occurs, is called the end
point/equivalent point. By plotting the change in conductance against the volume of base added we
will get a curve of two opposite straight lines.

19. Weak acid v/s weak base
• In the conical flask CH3COOH (weak acid) is taken as an analyte.
• In the burette NH4OH (weak base) is taken as titrant.
• CH3COOH is a weak acid so, it dissociates very slowly. It gives H+ and
CH3COO- ions. As the analyte dissociates first, instead of having high
conductance of H+ ion, at the starting stage of titration, the initial conductance
is very low.
• NH4OH is a weak base so, it dissociates very slowly. It gives NH4+ and OH-
ions.
• H+ ions and OH- will react and a neutralization reaction will take place,
which will form H2O.

20. Weak acid v/s weak base
• At first CH3COOH will be present in the conical flask, and the conductometer will trace its conductance,
which was very low. NH4OH is taken in the burette and added drop by drop. Neutralization reaction will take
place by replacing the H+ ions with OH- ions and water started to form. As the concentration of H+ ions
decreases, the conductance also decrease. After the compellation of neutralization reaction, there will be no
CH3COOH left. Then further addition of base from the burette, it will start the formation of ammonium
acetate, which is a strong electrolyte. And NH4OH will also dissociate, but in a very slow rate, which will
give OH- ions which is a highly conductive ion. The increase OH- ion will increase the conductance. But at a
certain point the concentration of CH3COOH ion will be sufficient enough to suppress the increase of
conductance. As a result, the conductance will remain constant. The point at which conductance starts to
show a horizontal line, is called the end point/equivalent point. By plotting the change in conductance
against the volume of base added we will get a curve of two straight lines.

21. Mixture of a Strong Acid and a Weak Acid vs. a
Strong Base or a Weak Base
• At first a mixture of strong acid and weak acid is present in the conical flask, as analyte.
• A strong/weak base is taken in the burette as titrant.
• At the starting point of the titration the initial conductance is very high because of the presence of strong
and weak acid, which gives H+ ions in a very high amount. So, the conductance is very high.
• At the beginning of the conductometric titration, the conductance will decrease because of the
neutralization reaction between H+ ions and OH- ions.
• After a certain point the first break point arises, due to the complete neutralization of strong acid.

22. Mixture of a Strong Acid and a Weak Acid vs. a
Strong Base or a Weak Base
• When the strong acid has been completely neutralized only then the weak acid starts neutralizing.
• As the weak acid forms salts, which are quite strong electrolyte. So, it will dissociate quickly, as a
result a slight increase in the conductance can be seen. So, The second break point corresponds to
the complete neutralization of weak acid.
• After the second equivalent/end point the conductance increases due to the excess of OH- ions, if
the titrant is a strong base.
• Or, After the second equivalent/end point the conductance remains constant due to the common ion
effect, if the titrant is a weak base.

23. Common Ion Effect
• When NaCl and KCl are dissolved in the same solution, the Cl- ions
are common to both salts.
• In a system containing NaCl and KCl, the Cl- ions are common ions.
Adding a common ion prevents the weak acid or weak base from
ionizing as much as it would, without the added common ion.
• The common ion effect suppresses the ionization of a weak acid by
adding more of an ion that is a product of this equilibrium.

24. Why does the conductivity of the solution
change quickly after the equivalence point?
• After the equivalence point of a conductometric titration process is reached, the
further addition of the titrant creates an excess of titrant ions, usually the excess of
hydroxide ions. As the conductance depends on the mobility of ions, the mobility of
this ions are high, which results in an increase in the conductivity of the solution.
• For example, when NaOH is added to a solution of HCl, the concentration of
hydroxyl ions (OH-) will increase after the endpoint is reached, thereby increasing
the conductivity.

25. Factors affecting conductometric measurement
• Temperature: The conductance of an electrolyte solution increases with increase in the
temperature due to increase in the extent of ionization.
• Nature of electrolyte: The strong electrolytes undergo complete ionization and hence
show higher conductivities since they furnish more number of ions. Whereas weak
electrolytes undergo partial ionization and hence show comparatively low conductivities
in their solutions.
• Viscosity of electrolyte: The ionic mobility is reduced in more viscous solvents. Hence
the conductivity decreases.
• Concentration of electrolyte: The specific conductance (κ) increases with increase in
concentration of solution as the number of ions per unit volume increases.
• Charge of the ions: Negative charge of the ions increases the conductivity where as the
positively charged ions decreases the conductivity.

26. Factors affecting conductometric measurement
• Ionic size & mobility: The ionic mobility decreases with increase in its size and hence
conductivity also decreases. E.g. In molten state, the conductivities of lithium salts are greater than
those of cesium salts since the size of Li + ion is smaller than that of Cs + ion.
• Extent of Hydration: However, in aqueous solutions the extent of hydration affects the mobility
of the ion, which in turn affect the conductivity. Heavily hydrated ions show low conductance
values due to larger size. E.g. In aqueous solutions Li + ion with high charge density is heavily
hydrated than Cs + ion with low charge density. Hence hydrated Li + bigger than hydrated Cs + .
As a result, lithium salts show lower conductivities compared to those of cesium salts in water.

27. Conductor
• An electrical conductor is a substance in which electrical charge carriers, usually
electrons, move easily from atom to atom with the application of voltage.
• Examples: metals, copper, silver, gold, aqueous solutions of salts (i.e., ionic
compounds dissolved in water), graphite, and the human body.

28. Insulator
• Insulators are materials that stop electricity from flowing. Insulators prevents
people from touching the conductive wire and receiving a shock.
• An insulator prevents the current from flowing depends on the thickness and the
type of material it is made of.
• Examples: plastics, Styrofoam, paper, rubber, glass and dry air.

29. Resistor
• A resistor is an electrical component that limits the flow of electrical current in an
electronic circuit. Resistors are materials that make the electricity move with
some difficulty.
• Examples: Tungsten Wires, Nichrome Wires, Steel and Carbon

30. Specific conductance (Ƙ)
• Specific Conductance or conductivity is the conductance of a given solution
enclosed in a cell having two electrodes of unit area and are separated by 1cm
apart. It is denoted by Ƙ (kappa). Its unit is (ohm-1cm-1)
• Ƙ = 1/ρ [ρ =Specific resistance]
• Specific conductance is defined as the conducting capacity of a
solution of the dissolved electrolyte and the whole solution is being
placed between two electrodes are 1 sq. cm and length 1 cm

31. Equivalent conductance (Λ)
• Equivalent conductance is defined as the conductance of all the ions produced by
one gram equivalent of an electrolyte in a given solution. It is denoted by capital
lambda (Λ ). Its unit is (ohm-1cm2eqvt-1)
• Λ = Ƙ x V

32. Molar conductance (µ)
• Molar conductance of electrolyte is defined as the conductance due to one
mole of electrolyte. It is denoted by µ. Its unit is (ohm-1cm2mol-1)
• µ= Ƙ x V

34. Thank You….