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Electrolytic Conductivity

April 10, 2023 1Electrolytic Conductance

ElectrolytesElectrolytes

Substances whose aqueous solution does not conduct electricity are called non electrolytes.

Examples are solutions of cane sugar, glucose, urea etc.

Substances whose solution in water conducts electric current. Conduction takes place by the movement of ions.

Examples are salts, acids and bases.


Types of ElectrolytesTypes of Electrolytes

Strong electrolyte are highly ionized in the solution.

Examples are HCl, H2SO4, NaOH, KOH etc

Weak electrolytes are only feebly ionized in the solution.

Examples are H2CO3, CH3COOH, NH4OH etc


Difference between electronic Difference between electronic & electrolytic conductors& electrolytic conductors

(3) Conduction increases with increase in temperature

(3) Conduction decreases with increase in temperature

(2) Flow of electricity is due to the movement of ions

(2) Conduction is due to the flow of electron

(1)Flow of electricity takes place by the decomposition of the substance.

(1) Flow of electricity take place without the decomposition of substance.

Electrolytic conductorsElectronic conductors


Fig. 1. Illustration of electrochemical terms


H+ + 2e- H2 (hydrogen gas at the (-)cathode).

2Cl- - 2e- Cl2 (chlorine gas at the (+)anode).

Mechanism of electrolytic conduction and electrolysis

The overall reaction is2NaCl(aq) + 2H2O(l) 2Na+

(aq) + 2OH-(aq) + Cl2(g)+ H2(g)


Electrolysis of sodium chloride solution Electrolysis of sodium chloride solution

NaCl ↔ Na+ + Cl-

H2O ↔ H+ + OH-

At cathode At AnodeH+ + e- → H Cl- → Cl + e-

2H → H2 2Cl → Cl2

Electrolysis of copper sulphate solution using platinum electrodes

CuSO4 ↔ Cu2+ + SO42-

H2O ↔ H+ + OH-At cathode At Anode

Cu2+ + 2e- → Cu 2OH- → H2O + O + 2e- O + O→O2


Resistance refers to the opposition to the flow of current.

For a conductor of uniform cross section(a)and length(l); Resistance R,

a

l

l lR l and R R

a a

Where is called resistivity orspecific resistance.

ResistanceResistance


Ohm’s lawOhm’s law Metallic as well as electrolytic conductors obey Ohm’s law

which states the strength of current (I) flowing through a conductor is directly proportional difference (V) applied across the conductor and is inversely proportional to the resistance (R ) of the conductor

I = V/R R - Resistance in V/A = Ω (Ohm) V - Voltage or potential difference in Volts, V I - Current in Amperes, A

If a material has a resistance of 1 Ω, it means that when applying a potential difference of 1 V, the current in the material is 1 A.


ConductanceConductanceThe reciprocal of the resistance is called conductance. It is denoted by C.

C=1/R

Conductors allows electric current to pass through them. Examples are metals, aqueous solution of acids, bases and salts etc.

Insulators do not allow the electric current to pass through them.

Examples are pure water, urea, sugar etc.

Unit of conductance is ohm-1 or mho or Siemen(S)


Specific conductance 1

Specific Specific Conductivity Conductivity

K

ax Conductance

Unit of specific conductance is ohm–1cm–1

SI Unit of specific conductance is Sm–1 where S is Siemen

aBut ρ = R

Ka.R

l/a is known as cell constant

Conductance of unit volume of cell is specific conductance.


Equivalent ConductanceEquivalent Conductance

Where, k = Specific conductivity

V = Volume of solution in cc. containing one gram equivalent of the electrolyte.

It is the conductance of one gram equivalent of the electrolyte dissolved in V cc of the solution.

Equivalent conductance is represented by

Mathematically, k V

1000k

Normality


It is the conductance of a solution containing 1 mole of the electrolyte in V cc of solution. it is represented as .

Molar Molar conductanceconductance

Where V = volume solution in cc

Molar conductance

k = Specific conductance

M=molarity of the solution.

= k × V

=k x 1000/M


Effect of Dilution on Effect of Dilution on ConductivityConductivitySpecific conductivity decreases on dilution.

Equivalent and molar conductance both increase with dilution and reaches a maximum value.

The conductance of all electrolytes increases with temperature.

concentration, (m ole L )– 1 1 /2

CH COO H (weak electrolyte)3

KCl (strong electrolyte)


Relation between Relation between equivalent conductivity and equivalent conductivity and molar conductivity molar conductivity

μ = valency factor(or n - factor) × λ

i.e.

Molar conductivity = n- factor x equivalent conductivity


Kohlrausch’s Kohlrausch’s LawLaw

a c

Where are known as ionic conductance of anion and cation at infinite dilution respectively.

a cand

“Limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cation of the electrolyte.”


Application of Application of Kohlrausch’s lawKohlrausch’s law

(2). For obtaining the equivalent conductivities of weak electrolytes at infinite dilution.

(1). It is used for determination of degree of dissociation of a weak electrolyte.

v

Where,

v

represents equivalent conductivity at infinite dilution.

represents equivalent conductivity at dilution v.


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