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1. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
CONDUCTOMETRICTITRATION
Conductometric titration is a type of titration in which the electrolytic conductivity of the
reaction mixture is continuously monitored as one reactant is added. The equivalence point is the
point at which the conductivity undergoes a sudden change. Marked increases or decrease in
conductance are associated with the changing concentrations of the two most highly conducting
ions—the hydrogen and hydroxyl ions. The method can be used for titrating coloured solutions
or homogeneous suspension (e.g.: wood pulp suspension), which cannot be used with normal
indicators.
Acid-base titrations and redox titrations are often performed in which common indicators are
used to locate the end point e.g., methyl orange, phenolphthalein for acid base titrations and
starch solutions for iodometric type redox process. However, electrical conductance
measurements can also be used as a tool to locate the end point, e.g., in a titration of a HCl
solution with the strong base NaOH.
As the titration progresses, the protons are neutralized to form water by the addition of NaOH.
For each amount of NaOH added equivalent amount of hydrogen ions is removed. Effectively,
the mobile H+ cation is replaced by the less-mobile Na+ ion, and the conductivity of the titrated
solution as well as the measured conductance of the cell fall. This continues until the equivalence
point is reached, at which one obtains a solution of sodium chloride, NaCl. If more base is added,
an increase in conductivity or conductance is observed, since more ions Na+ and OH− are being
added and the neutralization reaction no longer removes an appreciable amount of H+.
Consequently, in the titration of a strong acid with a strong base, the conductance has a minimum
at the equivalence point. This minimum can be used, instead of an indicator dye, to determine the
endpoint of the titration. The conductometric titration curve is a plot of the measured
conductance or conductivity values as a function of the volume of the NaOH solution added. The
titration curve can be used to graphically determine the equivalence point.
For reaction between a weak acid-weak base in the beginning conductivity decreases a bit as the
few available H+ ions are used up. Then conductivity increases slightly up to the equivalence
point volume, due to contribution of the salt cation and anion.(This contribution in case of a
strong acid-strong base is negligible and is not considered there.)After the equivalence point is
achieved the conductivity increases rapidly due to the excess OH- ions.
“The determination of end point of a titration by means of conductivity measurements are known
as conductometric titrations.”

2. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
TYPES OF CONDUCTOMETRIC TITRATIONS:
 Acid-base titration
 Precipitation titration
 Replacement titration
 Redox (oxidation-reduction) titration
 Complexometric titration
I) Acid-base titrations: Hydrogen and hydroxyl ions move more easily than other
agents and this is the basis of acid base titrations.
a) Strong acid Vs Strong Base:
E.g., [H+ + Cl-] +[Na+ + OH-] ----> [Na+ + Cl-] + H2O
In the beginning, the acid concentration will be high and so H+ conductance is more.
But as NaOH is added, Na+ ions replace H+ ions. So the conductance decreases and at
neutralization there will be least conductivity. And as the NaOH concentration os
increased, again the conductivity increases because of OH- ions.
b) Strong acid Vs Weak Base:

3. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
E.g., [H+ + Cl-] + [NH4+ + OH-] ---> [NH4+ + Cl-] + H20
In this case, initially the conductance will be more because of H+ ions.
But if once the NH4+ OH- is added, H+ ions will be replaced by NH4+ ions and so the
conductivity decreases. As NH4OH is a weak base, it do not dissociate and so after
neutralization the conductivity do not increase.
c) Weak acid vs Strong Base:
e.g., [CH3COO-+ H+] + [Na+ + OH-] ---> [CH3COO- + Na+] + H2O
Take CH3COOH and is titrated with NaOH. Once we add NaOH, it still decreases and
then the conductivity will increase. And after neutralization, because of OH- ions, the
conductivity again increases.
d) Weak Acid vs Weak Base:
Initially, the conductance decrease and then raises until the end point is achieved.
The increase in conductance before the end point is due to formation of
CH3COONa. If excess of base is added then conductivity increases.
II) Replacement titrations: Initially the salt of weak acid and strong base is taken
and strong acid is gradually added. This results in the replacement of weak acid.
Initially the conductance will be raise very slowly and after the end point, suddenly
the conductivity will increase.

4. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
III) Precipitation titrations: In this type of titrations, the ion which is to be replaced
with another ion having less rate of flow. This gives wide variation in conductivity . In
this reaction between mgso4 and Ba(OH)2(both of them are not completely soluble)
initially conductance decreases but once the end point is reached, the conductivity
increases.
IV) Redox titrations: In these titrations, there will be reduction in the number of
hydrogen ions. So the conductivity will reduce as the number H+ ions are
decreased.
These are also useful for studying the complex compounds.
FACTORS AFFECTING CONDUCTIVITY:
 Size of ions
 Temperature
 Number of ions
 Charge of ions

5. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
1.Size of the ions: The conductivity of the solution is inversely proportional to the size of the
ions .If the size of the ions is increasing then the conductivity of the solution will decrease
because the mobility of the ions will decrease by increasing the size of the ions.
2. Temperature: By increasing the temperature, the mobility of the ions in the solution will
increase. So temperature has a direct effect on conductance of solution. E.g. by increasing the
temperature the conductance will increase and vice versa.
Molar conductance of various ions at infinite dilution at 25℃
ions molar conductance
K+
73.52
Na+
50.11
Li+
38.69
H+
349.82
Ag+
61.92
Cl-
76.34
Br-
78.4
OH-
198
RELATION OF SPECIFIC CONDUCTANCE ANDEQUIVALENT
CONDUCTANCE WITH ELECTROLYTES NATURE ANDCONCENTRATION:
 Upon dilution specific conductance decreases, while equivalent conductance and molar
conductance increases.
 Increase in equivalent conductance in case of a weak electrolyte is due to increase in the
number of ions.
Principles:
Principle of the conductometric titrations theory states that for dilutions that are infinite, ions act
independently and in the process contribute toward conductance of the solution. The principle
behind this theory states that anions and cations have different conductance values. Therefore, if

6. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
you add a solution of one electrode to another, the final conductance will rely on the occurrence
of reaction. But if there is no chemical reaction in the electrolyte solutions, there will be an
increase in the level of conductance.
Electrovalent compounds when dissolved in water ionised into cations and anions.
Weak electrolyte has low degree of ionisation and strong electrolytes have higher degree of
ionisation.
Conductivity of solution depends upon the number of ions present in the solution.
 Conductivityisameasure of abilityof anelectrolytetocarry current.
 Whenan electrovalentcompoundisdissolvedinwateritsplitsupintoionswhichcarrycurrent
throughthe solutionof electrolyte.
 Whenweakacid or weakbase isdissolvedinwatertheirdegree of ionizationislow.
 Conductivityof asolutiondependsuponionspresentinthe electrolyte.
 As the numberof ionsinelectrolyte decreasesthe conductivitydecreasesandwhenthe number
of ionsincreasesthe conductivityincreases.
 The pointfrom whichthe conductance remainsconstantisneutralizationpointwhichindicates
the endpointof the reaction.

7. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
 Normalityandstrengthof solutioncanbe calculatedfromnormalityequation.N1V1 =N2V2 and
Strength(gms/lit.) =Normality×Equivalentweight.
EXAMPLE:
 In thistitrationof weakacid(CH3COOH) andweakbase (NH4OH),there isdecrease inthe
conductance initiallyatthe beginningof titration,oncontinuationof titrationthe conductance
of solutionstartsincreasingandreachesa certainmaximumvalue andthenremainsconstant
evenafteradditionof NH4OHiscontinued.
Apparatus:
The two essential tools used in the conductometric titration theory include an apparatus for
measuring and studying conductivity changes and a conductivity cell that has dipping electrodes.
But if you are carrying out simple titration using this theory, you will need a dipping electrode, a
mechanical stirrer and a beaker of a suitable size. You will also require measuring circuits that
will assist you in preventing concentration changes as a result of reactions at the electrodes.
CONDUCTOMETRIC MEASURMENTS:
Here the electrical conducting capacity (which is because of ions) of the solution is measured
and it is the basis for analysis. The ions will move from cathode to anode based on the change in
either direction. Mobility is the measure of rate at which the ion on moving in solution on
application of electrical or because of the difference in concentration.
CalculationMethod:
To calculate the end-point of the conductometric titration method, you should plot the curve of
the conductometric titration in the usual way. Estimate the end-point by plotting two straight
lines using the usual graphical method.
APPLICATIONSOF CONDUCTOMETRY
It can be usedforthe determinationof:-

8. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
 Solubilityof sparinglysoluble salts
 Ionicproductof water
 Basicityof organicacids
 Salinity of seawater(oceanographicwork)
 Chemical equilibriuminionicreactions
 Conductometrictitration
ADVANTAGESOF CONDUCTOMETRIC TITRATIONS
 No needof indicator
 Coloredordilute solutionsorturbidsuspensionscanbe usedfortitrations.
 Temperature ismaintainedconstantthroughoutthe titration.
 End pointcan be determinedaccuratelyanderrorsare minimizedasthe endpointisbeing
determinedgraphically.
USES:
RECENT DEVLOPEMNTS
 In refinaryindustries.
 Estimationof polyelectrolyticsolution.
 Biotechnology.
 Microbiosensorsforenviromental monitoring.

9. PHYSICALCHEMISTRY ASSIGNMENT BSIIICHEMISTRY, RABIA AZIZ
Conclusion:
The electrical conductance of a solution is a measure of the solution’s ability to conduct
electricity. The ability of a solution to conduct electric current decreases as the resistance of the
solution increases. Electricity is conducted in a solution by ions of electrolytes. Conductance of
electrolytes increases with the increase of temperature and concentration of electrolytes. The
conductance of a solution is the sum of the conductance of all the ions in the solution. The
conductance of an ion in solution is related to the charge, size and concentration of the ion.
Conductometry can be used to locate the end point of the titration. Conductometric titration is
useful for acid-base, precipitation, and complexation titrations.