Conductometry is used to analyze ionic species and to monitor a chemical reaction by studying the electrolytic conductivity of the reacting species or the resultant products.

1. PHARMACEUTICAL ANALYSIS
UNIT-5
TOPIC: CONDUCTOMETRY
B.PHARM 1ST YEAR
PRESENTED BY:
MS. SHWETA SINGH
(Assistant Professor)
RBMI, Bareilly

2. CONTENTS
• Introduction
• Principle of conductometry
• Important definition and relations
• Factors affecting conductance
• Instrumentation
• Conductometric titration
• Application of conductometry

3. INTRODUCTION
• Conductometry is used to analyze ionic species and to monitor a
chemical reaction by studying the electrolytic conductivity of the
reacting species or the resultant products.
• It has notable applications in analytical chemistry. Conductivity
measurement can be performed directly using a conductivity meter or
conducting conductometric titration.
• Conductometric analysis of electrolytes is a long-time practice.

4. DEFINITION OF CONDUCTOMETRY
• 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 :
Concentration of ions
Temperature
Mobility/Movement of ions

5. PRINCIPLE OF CONDUCTOMETRY
• The main principle involved in this method is that the movement of
the ions creates electrical conductivity. The movement of the ions
mainly depends on the concentration of the ions.
• The electric conductance follows Ohms law which states that, the
strength of current (I) passing through the conductor is directly
proportional to potential difference/voltage (V) and inversely to
resistance (R).
I =V/R

6. IMPORTANT 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 conductor’s 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 cm2 surface area
(A), its unit is Siemens.
ρ = R. a/l
 Specific conductivity (kappa): conductivity offered by a substance of 1 cm length (l) and 1 cm2
surface area, its unit is Siemens cm-1
k =1 ⁄ ρ

7. Molar conductivity (µv): The conductance of the volume of the solution
containing a unit mole of electrolyte that is placed between two electrodes of a unit
area cross-section or at a distance of one cm apart. The unit of molar conductivity
is S m2 mol-1
Molar Conductivity = Specific Conductivity (k) X volume of solution containing 1
mole of electrolyte

8. FACTORS EFFECTING CONDUCTANCE
The conductance of the solution depends on:
• Temperature: Conductance increases by increasing the temperature.
• Nature of ions: Size, molecular weight, number of charges the ion carries.
• The concentration of ions: As the number of ions increases the conductance of
the solution increases. The concentrated electrolyte solution will have high
conductance as compared to the dilute electrolyte solution.
• The size of the electrodes.

9. INSTRUMENTATION
The instrument used for the measurement of conductance is known as a Conductometer.
It consists of :
I. Current source: Mechanical high-frequency AC generators are used as a current source.
• DC is not employed in conductance measurement because electrodes become polarized leading
to high cell resistance.
I. Conductivity meter:1)Digital display- Shows conductance
2)Calibrator- For calibration 0.001M KCl solution is used.
3)Power Switch- Allows AC to flow (on/off switch).
Ⅲ. Conductivity Cell: Made of Pyrex (composition of Pyrex SiO2, Al203, B2O3, Na2O, CaO) or
quartz (fused SiO2) and fitted with two platinum electrodes.
• It should be placed in a water vessel to maintain a constant temperature.
• Fitted with 2 electrodes: Cathode(-ve) - attract cation
Anode (+ve) – attract anion

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

11. CONDUCTOMETRIC TITRATIONS
PRINCIPLE
The determination of the endpoint 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 a change in the number and the mobility of ions.
At the endpoint 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. TYPES OF CONDUCTOMETRIC TITRATION
• Conductometric titrations are employed for a large number of titrations to determine the equivalence
point. Different types of conductometric titration are mentioned below, Conductance of H+ and OH-
ions is higher as compared to other ions.
1. Acid-Base titrations:
a) Strong acid-strong base (HCl vs NaOH)
b) Strong acid-weak base (HCl vs NH4OH)
c) Weak acid-strong base (CH3COOH vs NaOH)
d) Weak acid-weak base (CH3COOH vs NH4OH )
2. Precipitation titration
3. Non- aqueous titration
4. Redox titration

13. TYPES OF CONDUCTOMETRIC TITRATION
A. Acid-Base titration
1. Strong acid vs. Strong Base
• Strong acid (HCl) is taken in a conductometric quartz vessel and strong base (NaOH) is added slowly as a titrant in the
HCl analyte solution.
• Initially, the concentration of hydrogen ions (H+) is higher, and the solution of HCl shows higher conductance. After
the addition of NaOH; hydrogen ions (H+) react with hydroxide ions (OH-) of NaOH and the conductance of the
solution decreases as salt formation occurs.
• At the endpoint, the conductance of the solution is lowest because all hydrogen ions (H+) react with hydroxide ions
(OH-).
• After the end point, addition of NaOH enhances the conductivity of the solution due to presence of hydroxide ions
(OH-).
HCl + NaOH NaCl + H2O

14. 2. Strong acid vs Weak base
• Strong acid (HCl) is taken in a conductometric quartz vessel and weak base (NH4OH) is added slowly
as a titrant in the HCl analyte solution.
• Initially, the concentration of hydrogen ions (H+) is higher, and the solution of HCl shows higher
conductance. After the addition of NH4OH; hydrogen ions (H+) react with hydroxide ions (OH-) of
NH4OH and the conductance of the solution decreases as salt formation occurs.
• At the endpoint, the conductance of the solution is lowest because all hydrogen ions (H+) react with
hydroxide ions (OH-).
• After the end point, addition of NH4OH do not effect the conductance and remains constant due to
common ion effect between NH4OH and NH4Cl.
At end point: HCl + NH4OH NH4Cl + H2O
After end point: NH4Cl NH4
+ + Cl-
NH4OH NH4
+ + OH-
(Common ion effect)

15. 3. Weak acid vs. Strong base
• Weak acid (CH3COOH) is taken in a conductometric quartz vessel and weak base (NaOH) is added slowly as
a titrant in the analyte CH3COOH solution.
• Initially, the concentration of hydrogen ions (H+) is slightly higher and the solution of CH3COOH shows
slightly higher conductance because it is a weak acid and hence it disassociates partially. After the addition of
NaOH; hydrogen ions (H+) react with hydroxide ions (OH-) of NaOH and the conductance of the solution
decreases slowly as salt formation occurs.
• At the endpoint, the conductance of the solution is lowest because all hydrogen ions react with hydroxide
ions (OH-).
• After the endpoint, if NaOH is added, rapid enhancement in the conductivity of the solution takes place due
to the presence of hydroxide ions (OH-).
At end point: CH3COOH + NaOH CH3COONa + H2O
After end point: CH3COOH CH3COO- + H+
CH3COONa CH3COO- + Na
(Common ion effect)

16. 4. Weak acid vs. Weak base
• A weak acid (CH3COOH) is taken in a conductometric quartz vessel and a weak base (NH4OH) is added slowly
as a titrant in the analyte CH3COOH solution.
• Initially, the concentration of hydrogen ions (H+) is slightly higher and the solution of CH3COOH shows
slightly higher conductance because it is a weak acid and hence it disassociates partially. After the addition of
NH4OH; hydrogen ions (H+) react with hydroxide ions (OH-) of NH4OH and the conductance of the solution
decreases slowly as salt formation occurs.
• At the endpoint, the conductance of the solution is constant because the addition of weak NH4OH does not
give sufficient hydroxide ions (OH-) to further increase in conductance because it is weak base and hence
disassociates partially.
At end point: CH3COOH + NH4OH CH3COONH4 + H2O
After end point: CH3COONH4 CH3COO- + NH4
CH3COOH CH3COO- + H+
(Common ion effect)

17. B. Precipitation titration
• A strong electrolyte (NaCl) is taken in a conductometric quartz vessel and Silver nitrate (AgNO3) is
added slowly as a titrant in the NaCl analyte solution. Initially, conductance is shown due to the
presence of NaCl. After the addition of AgNO3; chloride ions are replaced by nitrate ions (NO3
-) and
the conductance of the solution is constant because both ions show the same conductance.
• At the end point conductance of the solution starts increasing because nitrate ions are in excess after
the addition of a small amount of AgNO3.
NaCl + AgNO3 AgCl + NaNO3

18. APPLICATIONS OF CONDUCTOMETRIC TITRATION
• To check water pollution in rivers and lakes.
• Solubility of sparingly soluble salts like AgCl, BaSO4 can be detected
• Determination of atmospheric SO2.
• Alkalinity of fresh water.
• Salinity of seawater (oceanography)
• Used to trace antibiotics.
• Deuterium ion concentration in water- deuterium mixture food microbiology- for tracing
microorganisms
• Tracing antibiotics
• Estimate ash content in sugar juices
• The purity of distilled and de-ionised water can be determined