conductometry its important relationships

1. CONDUCTOMETRY

2. Outline
• Conductometry introduction
• Important relationships
• Instrumentation
• Measurement
• Conductometric titrations
• Advantages
• Disadvantages
• Applications
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3. Conductometry
• Conductometry is the measurement of the electrical conductivity of a
solution.
Basic principle
• The main principle involved in this method is the movement of the
ions which creates the electrical conductivity.
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4. Important relationships
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5. conductance
• Conductance is the flow of electricity through electrolyte solution due to migration of ions by
applying potential difference between two electrodes
• It is denoted by G
• It is reciprocal of resistance
G=1/R
• Its unit is seimen or Ω-1
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6. Resistance R
• It is measure of conductor opposition to the
flow of electric charge
R = 1/G
• Its unit is ohm Ω
Specific resistance ρ
• Resistance offered by substance of 1m
length L and 1 sq.m area A
R α L/A
R = ρ L/A
• ρ is specific resistance
ρ = R A/L
• Its unit Is ohm m
L/A is cell constant
The cell constant is defined by the distance between the electrodes (l) and their cross-
sectional area (A)
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7. Specific conductance
• Specific conductance of an electrolytic solution is the conductance of
the solution enclosed between two electrodes 1 cm apart and 1
cm2 area.
• The specific conductance (conductivity), κ (kappa) is the reciprocal of
the specific resistance.
κ =1/ρ
The unit of specific conductance is siemen.cm-1
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8. Molar conductance
• molar conductivity can also be defined as the conducting power of all the ions that are
formed by dissolving a mole of electrolyte in a solution.
Λm = κ / C
• Where κ is the specific conductivity and c is the concentration in mole per litre.
• The unit of molar conductivity is S⋅m2⋅mol-1.
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9. Equivalent conductance
• It is defined as the conductance of solution containing 1-gram equivalent electrolyte and the
solution placed between two parallel electrolyte 1cm apart
Λ=κ V
If C is the concentration In gram equivalent per dm3 then volume containing one gram equivalent
of the solute is will be 1000/C m3
• Λeq will be
Λeq =κ 1000/Ceq
• Unit of Equivalent conduction is seimens.m2 per gram equivalent
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10. Ohms law
• Ohm's law states that the current through
a conductor between two points is directly proportional to
the voltage across the two points.
I = V/R
• where I is the current through the conductor in units
of amperes, V is the voltage measured across the conductor
in units of volts, and R is the resistance of the conductor in
units of ohms.
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11. Faraday laws of electrolysis
First law
• Michael Faraday reported that the mass m of
elements deposited at an electrode is directly
proportional to the chargeQ
m α Q
m/Q = Z
• Here, the constant of proportionality Z is called
the electro-chemical equivalent of the substance.
Thus, can be defined as the mass of the
substance deposited/liberated per unit charge.
Second law
• Faraday discovered that when the same amount
of electric current is passed through different
electrolytes/elements connected in series, the
mass of the substance liberated/deposited at the
electrodes in gram is directly proportional to their
chemical equivalent.
• m α E
• Chemical equivalent E = atomic weight / valency
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12. electrolysis
• Electrolysis ;The phenomenon of breakdown of an electrolyte by passing electric current
through its solution is termed Electrolysis.
• The process of electrolysis is carried in an apparatus called the Electrolytic cell. The cell
contains water-solution of an electrolyte in which two electrodes are dipped. These rods are
connected to the two terminals of a battery (source of electricity)
• The electrode connected to the positive terminal of the battery attracts the negative ions
(anions) and is called anode.
• The other electrode connected to the negative end of the battery attracts the positive ions
(cations) and is called cathode.
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13. Mechanism of
electrolysis
The cations migrate to the cathode and
form a neutral atom by accepting
electrons from it.
The anions migrate to the anode and
yield a neutral particle by transfer of
electrons to it.
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14. Example
• Let us consider the electrolysis of hydrochloric acid as an example.
• In solution, HCl is ionized,
• HCl → H + + Cl−
• At cathode:
H + + e– → H ......(Reduction, gain of electrons)
• At anode:
Cl– → Cl + e− ......(Oxidation, loss of electrons)
• The net effect of the process is the decomposition of HCl into hydrogen and chlorine gases.
• The overall reaction is:
2HCl → H2 + Cl2 ......(Decomposition)
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15. Effect of concentration on conductance
Specific conductance
• Specific conductance of strong or weak electrolyte decrease upon dilution
• Specific conductance is the conductance of 1 centimeter cube of solution .
Upon diluting , the concentration of ion per centimeter cube decreases and
therefore, conductivity decreases
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16. Effect of concentration on molar or
equivalent conductance
• Equivalent or molar conductance increase upon dilution
• The increase in molar or equivalent conductivity is due to fact it is product of
conductivity and volume of solution containing one mole or 1 gram
equivalent of electrolyte
Λ=κ V
• This increase in volume results increase in conductivity
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17. Nature of electrolyte
strong electrolyte
• Molar conductivity increase slowly upon dilution.
• Upon infinite dilution , conductivity
approaches limiting value when concentration
approaches zero.This is called molar conductivity
at infinite volume
• For molar conductance
Λm = Λm° - A√C
• A is experiment constant
• Λm° is molar conductivity at infinite dilution
• This equation is called Debye huckle Onsager
equation 17

18. Weak electrolyte
• Weak electrolytes dissociates very less so
low conductance as compared to strong
electrolyte
• But upon dilution , ions dissociates more
hence conductance value increase
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19. Effect of temperature
• Conductivity depends on mobility of ions , by increasing temperature mobility of
ions increases , hence conductivity increase . Experiment shows that conductance
increases 2-3 percent ,by increase in 1c°
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20. Effect of temperature on weak electrolyte
• For weak electrolyte , effect of temperature depends on enthalpy
change ΔH.
• If ionization value is -ΔH, process will be exothermic , conductance
decreases
• If ionization value is +ΔH , process will be endothermic , conductance
increases
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21. Instrumentation
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22. Conductometer
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23. CONDUCTOMETER
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24. Current source
• Alternating current source is used
• High frequency alternating current generator is employed
• Electrical potential is applied ; ions will be transferred and ultimately conductance takes
place
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25. Conducting meter
• Digital display
• Calibrator
• Power switch
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26. Electrodes
• Electrodes are made up of platinum
• Distance between electrodes is 1 cm
• Area of electrode surface is 1cm2 .
• Electrodes are coated with platinum black to avoid polarization and to increase surface area
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27. Distance between electrodes is adjusted depending
upon the conductance of the solution.
• For the solutions of high conductance, the electrodes are widely spaced
• For the solutions of low conductance, the electrodes are close to each other
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28. Conductivity cell
The solution whose conductance is to be determined is placed in a special type of cell known as
conductivity cell.
Composition of conductivity cell:
• Made up of glass such as Pyrex or of quartz glass
• Platinum electrodes coated with the finely divided platinum black
• Mercury for connection
• Thermostats for regulating temperature
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29. Measurement of conductance:
• As we know that conductance is reciprocal of resistance.
• Conductance of ionic solutions is measured by measuring the resistance of solution in a cell.
• This can be done by using a wheat stone bridge .
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30. Wheat stone bridge:
• An electrical bridge consisting of two branches of a parallel circuit joined by a galvanometer
and used for determining the value of an unknown resistance in one of the branches.
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31. Working of a wheat stone bridge:
• The Wheatstone bridge works on the principle of null deflection, i.e., the ratio of their
resistances are equal and no current flows through the circuit.
• Wheatstone bridge, also known as the resistance bridge, calculates the unknown
resistance by balancing two legs of the bridge circuit. One leg includes the component of
unknown resistance.
• Thus, by knowing resistance we can find out conductance.
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32. Conductometric titrations:
• 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.
Principle of conductometric titrations:
• It works on the principle that the difference in the volume of ions leads to a difference
in the conductivity of both ions.
The graph obtained gives us the equivalence point .
Equivalence point :
The equivalence point is the point at which the conductivity undergoes a sudden change.
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33. Types of conductometric titrations:
1 –Acid base titration
• Strong acid with strong base
• Weak acid with strong base
• Strong acid with weak base
• Weak acid with weak base
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34. Strong acid with strong base
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
Equation:
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
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35. 35

36. Weak acid with strong base:
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.
Equation :
CH3COOH (aq) + NaOH (aq) → CH3COONa (aq) + H2O (l)
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37. 37

38. Strong acid with weak base:
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 ionized in the presence of ammonium sulphate
Equation:
2 NH3 (aq) + H2SO4 (aq) → (NH4)2SO4 (aq)
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39. 39

40. Weak acid with weak base:
• Ammonium hydroxide (NH4OH) and Acetic acid (CH3COOH).
For weak acid and weak base, the conductance initially rises due to the formation of a salt, say
ammonium ethanoate from Ammonium hydroxide (NH4OH) and Acetic acid (CH3COOH). On
further addition of NH4OH, the conductance continually raises till the neutral point is reached.
After this, the conductance remains almost constant because NH4OH is a very weak base and
contributes only very slightly to conductance.
Equation:
NH4OH + CH3COOH → CH3COONH4 + H2O
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41. 41

42. Advantages of acid base titration:
• It does not require special or expensive chemicals.
• It does not require sophisticated instruments
• The methods are generally robust.
• Cost-effective
• Does not require high expertise, has a simple operating procedure.
• Time saving technique
• Different types of titrations are available for different types of samples (analytes)
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43. Disadvantages of acid base titrations:
• The theory cannot explain basic compounds that do not contain the hydroxide ion.
• Require specific pH range
• Consumes large amount of chemicals being analyzed
• It requires reaction to take place in a liquid phase; it is not suitable for solids or
solutes which have solubility issues.
• Results in a large amount of chemical waste that must be disposed off
• It has limited accuracy and precision
• Since this is an open system, temperature, moisture (humidity) and some
environmental factors can affect the results.
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44. 2- Precipitation titration:
• 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 the concentration of silver as well as nitrate ions.
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45. Advantages of precipitation titration:
• Used to determine the halide ions.
• To measure salt content in various food & beverages.
• To analyze various drugs.
• For analyzing the concentration of the anion in the analyte.
Disadvantages of precipitation titration:
• Only very few halide ions can be titrated by using precipitation titration method.
• Coprecipitation also occurs.
• The endpoint is very difficult to analyze.
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46. ComplexometricTitration
Definition
• Complexometric titration is a form of volumetric analysis in which the formation of a colored
complex is used to indicate the end point of a titration.
Purpose
• Complexometric titrations are particularly useful for the determination of a mixture of
different metal ions in solution
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47. Common indicators for complexometric
Titration
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48. Reagent used in
complexometric
titrations
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49. Complexometric titration in terms of
conductometry
Reaction at start
• The conductance is very high due to metal ions(ligands)
During reaction.
• The conductance gradually decrease during the reaction due to
complex formation
At the end of reaction.
• The conductance give constant value because all ions will combined
with complexing reagent and participate are formed.
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50. Graphical Representation
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Conductance
EDTA used

51. Application of complexometric titration
• The complexometric titration is used to determine the
concentration of metal ions in sample solutions.
• It is used for the estimation of the amount of calcium present in
food product
• It is used to find out the total hardness of the water.
• It is used in analytical chemistry to perform the assay.
• Used in environmental analysis to determine bad metals.
• Cosmetic products are also analyzed.
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52. Advantages of conductometry
• The measurement process of conductivity is simple.
• Broad selectivity.
• Indicators are not required.
• It is suitable for the turbid suspensions, diluted, and colored solution.
• By graph plotting, the endpoint can be determined.
• Provide accurate results with minimum errors.
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53. Disadvantages of conductometry
• Conductometric titration technique, only a few specific redox
titrations can be carried out.
• It shows less accurate results when the total electrolytic
concentration is high in the solution.
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54. Application of conductometry
• Used to determine the purity of water by checking the pollution.
• It can be used for determination of sparingly soluble salt
• Conductometry is also used in the food industry by microbiologists
in order to trace microorganisms.
• Application of conductometry is also found in the pharmaceutical
industry.
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55. Cond…..
• It is used to check the basicity of organic acids and to detect
antibiotics.
• It can be used for determination of salinity of sea water (
oceanographic work)
• Used in the quantitative analysis of the compounds.
• Determination of atmospheric contaminants in air
(SO2,NO3,acicdic rain etc. )
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