Electrochemistry

Electrolysis and Electrical Conductance

- Electrolytes and Non-electrolytes

- Electrolysis and it’s mechanism

-Electrical Units- Coulomb- Ampere- Ohm- Volt

Faraday’s Law of Electrolysis

First Law:The amount of a given product liberated at an electrodeduring electrolysis is directly proportional to the quantityof electricity which passes through the electrolyte solution.

Second Law:When the same quantity of electricity passes through solutions of different electrolytes, the amounts of the substances liberated at the electrodes are directly proportional to their chemical equivalents.

The electrical Unit Faraday

The quantity of electricity required to liberate one gram-equivalent of a substance is 96,500 coulombs. This quantity of electricity is knownas Faraday (F).

1 Faraday = 96, 500 coulombs = 1 Mole electrons

Conductance or Conductivity

The power of electrolytes to conduct electric currents is termed as conductivity or conductance.

I = E / R, where I= current flow, E=potential differences at two ends, R=resistance

Specific resistance:

R α l / A R = ρ x l/A

Specific conductance:The conductance of one centimeter cube (cc) of a solutionof an electrolyte.

Κ = 1 / ρ

Equivalent conductanceThe conductance of an electrolyte obtained by dissolvingone gram-equivalent of it V cc of water.

Λ = κ x V

Molar conductanceThe conduction of all ions produced by one mole (one gram-molecular weight) of an electrolyte when dissolved in a certain volume V cc.

μ = κ x V

Molar Conductance ( Unit)

Kohlrausch’s Law

The equivalent conductance of an electrolyte at infinite dilution is equal to the sum of the equivalent conductances of the component ions.

λ∞ = λa + λc

Ostwald’s Dilution Law

Limitation:Holds good only for weak electrolytes and fails completely whenapplied to strong electrolytes.

Electrochemical Reactions

In electrochemical reactions, electrons are transferred from one species to another.

Electrochemical CellsA device for producing an electrical current from a

chemical reaction (redox Reaction) is called an electrochemical cell.

How a Redox reaction can produce an electrical current?

Electromotive Force (emf)

• Water only spontaneously flows one way in a waterfall.

• Likewise, electrons only spontaneously flow one way in a redox reaction—from higher to lower potential energy.

• The potential difference between the anode and cathode in a cell is called the electromotive force (emf).

• It is also called the cell potential, and is designated Ecell.

Ecell = Ered (cathode) − Ered (anode)

Single electrode potential:The potential of a single electrode in a half-cell is called the single electrode potential.

Standard EMF of a cell (Eᴼ)The emf of a cell with 1 M solutions of reactants and productsIn solution measured at 25 ᴼC.

Voltaic CellsA voltaic cell is one in which electrical current is generatedBy a spontaneous redox reaction.

- Predicting the oxidizing or reducing ability

- Predicting whether a metal will displace another metal from it salt or not

THE NERNST EQUATION

Multiple Choice Questions

Question 1. The conductivity of an electrolyte is due to thea) Presence of ions in the electrolyteb) free movement of ions in the solutionc) reunion of ions in the solutiond) release of heat energy due to ionisation

Key : (b)

Question2. The electrical conductivity of an electrolyte depends upona) The number of molecules in the electrolyteb) the number of ions present in the electrolytec) the number ions present in the solutiond) the number of molecules of the solvent

Key: (c)

Question 3. Ostwald’s dilution law is applicable toa) All electrolytesb) strong electrolytesc) weak electrolytesd) non-electrolytes

Key (C)

Question 4. The site of oxidation in an electrochemical cell isa) The anodeb) the cathodec) the electroded) the salt bridge

Key : (a)

Question 5. The salt bridge in the electrochemical cell serves toa) Increase the rate at which equilibrium is attainedb) increase the voltage of the cellc) maintain electrical neutralityd) increase the oxidation/reduction rate

Key : (C)