Strong electrolyte are highly ionized in the solution.
Examples are HCl, H 2 SO 4 , NaOH, KOH etc
Weak electrolytes are only feebly ionized in the solution.
Examples are H 2 CO 3, CH 3 COOH, NH 4 OH etc
April 15, 2011 Electrolytic Conductance
Difference between electronic & electrolytic conductors April 15, 2011 Electrolytic Conductance (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 conductors Electronic conductors
Fig. 1. Illustration of electrochemical terms April 15, 2011 Electrolytic Conductance
Mechanism of electrolytic conduction and electrolysis The overall reaction is 2 Na Cl (aq) + 2 H 2 O (l) 2 Na + (aq) + 2 OH - (aq) + Cl 2 (g) + H 2 (g) April 15, 2011 Electrolytic Conductance H + + 2 e - H 2 ( hydrogen gas at the ( - ) cathode ). 2 Cl - - 2 e - Cl 2 ( chlorine gas at the ( + ) anode ).
Electrolysis of sodium chloride solution NaCl ↔ Na + + Cl - H2O ↔ H + + OH - At cathode At Anode H + + e- -> H Cl - -> Cl + e- 2H -> H 2 2Cl -> Cl 2 Electrolysis of copper sulphate solution using platinum electrodes CuSO4 ↔ Cu2+ + SO 4 2- H2O ↔ H+ + OH- At cathode At Anode Cu2+ + 2e- -> Cu 2OH- -> H2O + O + 2e- O + O->O2 April 15, 2011 Electrolytic Conductance
Resistance Resistance refers to the opposition to the flow of current. For a conductor of uniform cross section(a) and length(l); Resistance R, April 15, 2011 Electrolytic Conductance a l Where is called resistivity or specific resistance.
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.
April 15, 2011 Electrolytic Conductance
Conductance The 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) April 15, 2011 Electrolytic Conductance
Specific Conductivity Unit of specific conductance is ohm –1 cm –1 SI Unit of specific conductance is Sm –1 where S is Siemen l/a is known as cell constant Conductance of unit volume of cell is specific conductance. April 15, 2011 Electrolytic Conductance Specific conductance x Conductance
Equivalent Conductance Where, k = Specific conductivity V = Volume of solution in cc. containing one gram equivalent of the electrolyte. April 15, 2011 Electrolytic Conductance It is the conductance of one gram equivalent of the electrolyte dissolved in V cc of the solution. Equivalent conductance is represented by Mathematically,
Molar conductance It is the conductance of a solution containing 1 mole of the electrolyte in V cc of solution. it is represented as . Where V = volume solution in cc Molar conductance k = Specific conductance M=molarity of the solution. =k x 1000/M April 15, 2011 Electrolytic Conductance
Effect of Dilution on Conductivity Specific 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. April 15, 2011 Electrolytic Conductance
Relation between equivalent conductivity and molar conductivity i.e. Molar conductivity = n- factor x equivalent conductivity April 15, 2011 Electrolytic Conductance
Kohlrausch’s Law “ Limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cation of the electrolyte.” April 15, 2011 Electrolytic Conductance Where are known as ionic conductance of anion and cation at infinite dilution respectively.
Application of Kohlrausch’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. Where, April 15, 2011 Electrolytic Conductance represents equivalent conductivity at infinite dilution. represents equivalent conductivity at dilution v.