It is an electrochemical method of analysis used for the determination or measurement of the electrical conductance of an electrolyte solution by means of a conductometer. Electric conductivity of an electrolyte solution depends on : Type of ions (cations, anions, singly or doubly charged Concentration of ions Temperature Mobility of ions The main principle involved in this method is that the movement of the ions creates the electrical conductivity. The movement of the ions is mainly depended on the concentration of the ions. The electric conductance in accordance with ohms law which states that the strength of current (i) passing through conductor is directly proportional to potential difference & inversely to resistance. i =V/R

1. Conductometry
DR. RUPINDER KAUR
ASSOCIATE PROFESSOR
DEPT. OF PHARMACEUTICAL CHEMISTRY
ISF COLLEGE OF PHARMACY
WEBSITE: - WWW.ISFCP.ORG
EMAIL: RUPINDER.PHARMACY@GMAIL.COM
ISF College of Pharmacy, Moga
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Internal Quality Assurance Cell - (IQAC)

2. Introduction
 It is an electrochemical method of analysis used for the determination or
measurement of the electrical conductance of an electrolyte solution by means of a
conductometer.
 Electric conductivity of an electrolyte solution depends on :
• Type of ions (cations, anions, singly or doubly charged
• Concentration of ions
• Temperature
• Mobility of ions
2

3. 3Principle
 The main principle involved in this method is that the movement of the ions creates
the electrical conductivity. The movement of the ions is mainly depended on the
concentration of the ions.
 The electric conductance in accordance with ohms law which states that the strength
of current (i) passing through conductor is directly proportional to potential
difference & inversely to resistance.
i =V/R

4. 4Important Definitions and Relations
 Conductance (G): ease with which current flows per unit area of conductor per
unit potential applied & is reciprocal to resistance (R) , its unit is Siemens (ohm-1)
G = 1⁄ R
 Resistance (R): is a measure of the conductors opposition to the flow of electric
charge, its unit is ohm.
R =1/G
 Specific resistance (ρ): resistance offered by a substance of 1 cm length (l) and 1
sq.cm surface area (A), its unit is ohm cm
ρ = aR/l
 Specific conductivity (kv): conductivity offered by a substance of 1 cm length (l)
and 1 sq. cm surface area, its unit is mhos cm-1
kv =1 ⁄ ρ

5. 5
 Equivalent conductivity (λv): conductivity of a solution containing equivalent
weight of the solute between electrodes 1 cm apart and 1 sq. cm surface area, its
unit is mhos cm-1
Equivalent conductivity = specific conductivity (kv) X volume of solution
containing 1 gram equivalent weight of electrolyte
 Molar conductivity (µv): conductivity of a solution containing molecular weight of
the solute between electrodes 1 cm apart and 1 sq. cm surface area
Molar conductivity = specific conductivity (kv) X volume of solution containing 1
molecular weight of electrolyte

6. 6The conductance of the solution depends on:
• Temperature: It is increased by increase of temperature.
• Nature of ions: size, molecular weight, number of charges the ion carries and other
factors
• The concentration of ions: As the number of ions increases the conductance of the
solution increases.
• The size of the electrodes
G = kv A/L
kv = G L/A
L/A is cell constant
K is the specific conductance or conductivity
ohm-1cm-1 or seimen/cm.

7. 7
The instrument used for measurement of conductance are know as conductometers. It
consists of :
 Current source
• Mechanical high frequency AC generator by Washburn .
• DC current is not employed in conductance measurement because electrodes
becomes polarised leading to high cell resistance.
 Conductivity cells
• Made of pyrex or quartz and are fitted with two platinum electrodes.
• Should be placed in vessel containing water to maintain constant temperature
• Types :
1. Wide mouthed cell
2. Cell for reactions producing precipitation
3. Dip type cells
Instrumentation

8. 8
 Electrodes:
• Platinum sheets, each of 1 cm2 are fixed at distance of
1 cm
• The surface is coated with platinum black to avoid
polarization effects and increase effective surface area.
• Platinisation of electrodes is done by coating solution of 3% chlorplatinic
acid and lead acetate on it to get uniform coating.
• Electrodes usage depends on conductivity and concentration.
• If conc is low then electrodes should be largely and closely packed.

9. 9
 The instrument used to measure conductance is
called conductance bridge or conductometer.
 Classical circuit employed for measurement is
wheatstone bridge.
 Various types are:
• Kohlrausch conductance bridge
• Direct reading conductance bridge
• Phillips conductance bridge
• Mullard’s conductance bridge
• Pye’s conductance bridge
Measurement

10. 10
Hence, conductivity of unknown solution:
1 ⁄ R2 =NL ⁄ ML × R1
The measured conductivity (1/R1) is not always equal to the specific conductivity
of solution , because the physical configuration of platinum electrode i.e, length
and area of electrodes varies from one another . Hence conductivity of solution is
obtained by calculating a factor called “cell constant”.
Cell constant: Defined as ratio of distance between the two electrodes(l) to the
area of electrodes(A)
Therefore,
θ =1 ⁄ A

11. 11Conductometric 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 the
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.

12. 12Types of conductometric titrations
Acid –base or neutral titrations
Strong Acid with a Strong Base, e.g. HCl with NaOH
• When the base is added in HCl solution,
the conductance falls due to the
replacement of hydrogen ions by the
added cation as H+ ions react with OH −
ions to form undissociated water.
• After the equivalence point, the
conductance increases due to the large
conductivity of OH- ions

13. 13
Weak Acid with a Strong Base, e.g. acetic acid with NaOH
• Initially the conductance is low due to
the feeble ionization of acetic acid,
followed by increase due to NaOH
• Beyond the equivalence point, steep rise
due to excess of NaOH.

14. 14
Strong Acid with a Weak Base, e.g. sulphuric acid with dilute ammonia
• Initially the conductance is high and then
it decreases due to the replacement of H+.
• But after the endpoint has been reached
the graph becomes almost horizontal,
since the excess aqueous ammonia is not
appreciably ionised in the presence of
ammonium sulphate

15. 15
Weak Acid with a Weak Base, e.g. sulphuric acid with dilute ammonia
• The nature of curve before the
equivalence point is similar to the curve
obtained by titrating weak acid against
strong base.
• After the equivalence point, conductance
virtually remains same as the weak base
which is being added is feebly ionized
and, therefore, is not much conducting

16. 16
Precipitation Titrations
• eg Potassium chloride Vs Silver nitrate
KCl + AgNO3 AgCl + KNO3
• When silver nitrate added, the first part of the curve
shows no increase in conductivity as there is only
replacement of chloride ions with nitrate ions.
• After end point conductivity increases because of
increase in cthe concentration of silver as well as
nitrate ions.

17. 17
 Determination of specific conductivity is not required.
 No indicator is necessary.
 Suitable for coloured or dilute solutions.
 Since end point is determined by graphical means accurate results are obtained with
minimum error.
 Used for analysis of turbid suspensions, weak acids, weak bases, mix of weak &
strong acids.
 Temperature need not be known provided it is maintained constant throughout the
titration.
Advantages of conductometric titrations

18. 18
 Increased level of salts in solution masks the conductivity changes , in such cases
it does not give accurate results.
 Application of conductometric titrations to redox systems is limited because, high
concentrations of hydronium ions in the solution tends to mask the changes in
conductance
Disadvantages of conductometric titration

19. 19
Solubility of sparingly soluble salts like AgCl, BaSO4 can be detected
 Check water pollution in rivers and lakes.
 Alkalinity of fresh water.
 Salinity of sea water (oceanography)
 used to trace antibiotics.
 Deuterium ion concentration in water- deuterium mixture
 Food microbiology- for tracing micro organisms
 Tracing antibiotics
 Estimate ash content in sugar juices
 Purity of distilled and de -ionised water can determined
 Determination of atmosphericSO2,etimation of vanillin in vanilla flavour
Applications