DEFINITION :- Conductometry is defined as determination or measurement of the electrical conductance of an aq. electrolyte solution by means of a conductometer.
PRINCIPLE :- It is based on the conductance of electrical current by aqueous electrolyte solutions in a manner similar to that of metallic conductors.
The electrical conductance is in accordance with the ohm′s law which states the strength of current passing through a conductor (in this case electrolyte solution.) is directly proportional to the potential difference applied across the electrodes and inversely proportional to the resistance offered by the conductor
R= resistance (ohms Ω)
SOME IMPORTANT TERM DEFINITION :-
1.SPECIFIC CONDUCTANCE (K):– Specific conductance of a homogenous body may be defined as the conductance of the body of uniform length and uniform area of cross section(A).
I.E. Gα A/L
K= G L/A
WHERE, K = SPECIFIC CONDUCTANCE
UNITS :- Ohm– cm–
Specific conductance is also defined as reciprocal of specific resistance.
2.Molar conductance (λ) :– It is defined as the conductance of a solution containing 1 mole of the solute in 1000 cm3 of the solution which is placed between two parallel electrodes which are are 1 cm apart.
K = specific conductance (ohm-1 cm-1)
C = molar concentration (moles/cm3)
UNITS :- Ohm-1 cm2 mol-1
3.Equivalent conductance (λeq):- It is defined as the specific conductance (k) of a solution containing 1 gm equivalent of solute in 1000 cm3 of solution.
λeq = 1000k/ceq
k= specific conductance
ceq = Equivalent concentration
unit :- ohm-1 cm2 equiv-1
4. Ohm′s Law :- the current flowing in a conductor is directly proportional to the applied electromotive force and inversely proportional to the resistance of the conductor
5. Kohlrausch law :- At infinite dilution each ion contribute definite amount of conductance to total conductance irrespective nature of other ions.
CONDUCTOMETRY THEORY :-
- In conductometric titration the end point is detected by measuring the change in the electrical conductance of the solution which is being titrated.
- Generally the conductometric titrations is based on the conduct of a solution and depends on the concentration and conductive of the ions.
- It is also based on the substitutions of one mobility by the ion of another mobility.
Addition of HCl to ammonium hydroxide
H+ Cl– + NH4+ OH– → NH4Cl + H2O
The high conductivity H ions (350) are replaced by low conductivity NH4 ions (73).
FACTORS AFFECTING CONDUCTANCE :-
|No.||factor||Effect on conductance|
|1.||Type of current||Always A.C is used to prevent polarization of electrode in conductivity. As the frequency of current increases, conductance increases.|
|2.||Type of solute||Strong electrolytes have higher conductance.|
|3.||Charge on ions||As ionic change increases molar conductance increase (SO+2 Cl–)|
|4.||Size of ions||As the size of ions increases, conductance decrease|
|5.||Mobility of ions / Spread of ions||Absolute velocity of any ion under influence of 1 volt potential per cm is called ionic mobility.|
|6.||Viscosity||High viscosity low conductance|
|7.||Temperature||High temperature High conductance 1 C rise in temp. cause 2% rise in mobility of ions.|
APPLICATION OF CONDUCTOMETRY :-
- Finding conductance of unknown compound.
- salt analysis.
- Ionic product of water.
- Determination of solubility and Ksp of sparingly soluble compound.
- Determination of mode of ionization of complex compound.
- Conductometric titration & precipitation titrations.
- Purity of water.
1. Which is working principal of conductometry ?
a. measurement of potention.
b.measurement of conductivity of solution.
c.measurement of emf.
d. none of the above
2. which equation is explained ohm′s law ?
a. K= G L/A
c.λeq = 1000k/ceq
3.”The specific conductance (k) of a solution containing 1 gm equivalent of solute in 1000 cm3 of solution.” this sentence shows which term definition?
d. Equivalent conductance (λeq)
4. Which is not application of conductometry ?
a. determine of moisture and water contain
b.Purity of water
c.Ionic product of water.
d. Conductometric titration & precipitation titration
5. In conductometry solution if temp. is increase by 1ºc
a.1% rise in mobility of ions.
b.2% rise in mobility of ions.
c.3% rise in mobility of ions.
d.4% rise in mobility of ions.
6.Kohlrausch law is
a.the current flowing in a conductor is directly proportional to the applied electromotive force and inversely proportional to the resistance of the conductor
b.At infinite dilution each ion contribute definite amount of conductance to total conductance irrespective nature of other ions.
c.Specific conductance of a homogenous body may be defined as the conductance of the body of uniform length and uniform area of cross section(A)
d.It is defined as the conductance of a solution containing 1 mole of the solute in 1000 cm3 of the solution which is placed between two parallel electrodes which are are 1 cm apart.
7. if the ion size is decrease in solutions
c.a and b
d.none of the above
ANSWER KEY :-
TEXT BOOK OF PHARMACEUTICAL ANALYSIS THIRD EDITION DR. S. RAVI SANKAR (PAGE NO.10.1-10.6)