This document provides an introduction to electrochemistry and discusses key concepts such as electrolytes, electrolytic cells, and the preferential discharge theory of electrolysis. Some main points:
1) Electrolytes are substances that undergo decomposition into ions when an electric current is passed through them in solution. Electrolytic cells, also called voltameters, are devices used to carry out electrolysis where electrical energy is converted to chemical energy.
2) During electrolysis, oxidation occurs at the anode where anions are released and reduction occurs at the cathode where cations gain electrons. The preferential discharge theory states that ions with lower discharge potentials will be discharged first at the appropriate electrode.
3) Examples of products formed
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CONTENTS
Electrochemistry: definition & importance
Conductors: metallic & electrolytic conduction,
Electrolytes, Electrochemical cell & electrolytic cell
A simple electrochemical cell: Galvanic cell or (Daniell Cell)
Cell reaction, cell representation, Salt bridge & its use,
Electrode potential, standard electrode potential, SHE,
Standard cell potential or standard electromotive force of a cell
Electrochemical series (Standard reduction potential values)
Nernst Equation, Relationship with Standard cell potential with Gibbs energy & also equilibrium constant
Resistance (R) & conductance (G) of a solution of an electrolyte
Conductivity (k) of solution, Cell constant (G*) & their units,
Molar conductivity (Λm) & its variation with concentration & temperature,
Debye Huckel Onsager equation & Limiting molar conductivity,
Kohlrausch’s law & its application & numerical problems.
Electrolytic cells & electrolysis.
Some examples of electrolysis of electrolytes in molten / aq. state.
Faraday’s laws of electrolysis: First & second law- numerical problems. Corrosion, Electrochemical theory of rusting.
Prevention of rusting.
Conductors and Non-Conductors
Substances can be classified as conductors and non-conductors based on their ability to conduct electricity.
Conductors: Substances that allow electric current to flow through them are called conductors. For example, Plastic, Wood, etc.
Non-Conductors: Non-conductors are insulators that do not allow electricity to pass through them. For example, Copper, Iron, etc.
Types of Conductors
Conductors are divided into two groups: Metallic conductors and Electrolytes.
Metallic Conductors: These conductors conduct electricity by the movement of electrons without any chemical change during the process. This type of conduction happens in solids and in the molten state.
Electrolytes: They conduct electricity by the movement of the ions in the solutions. It is present in the aqueous solution.
Distinguish between Metallic and Electrolytic Conduction
Metallic Conduction Electrolytic Conduction
The movement of electrons causes the electric current The movement of ions causes the electric current
There is no chemical reaction Ions get ionised or reduced at the electrodes
There is no transfer of matter It involves the transfer of matter in the form of ions
Follows Ohm’s law Follows Ohm’s law
Resistance increases with an increase in temperature Resistance decreases with an increase in temperature
Faraday’s law is not followed Follows Faraday’s law
Electrolytes
(a) Substances whose aqueous solutions allow the conductance of electric current and are chemically decomposed are called electrolytes.
(b) The positively charged ions furnished by the electrolyte are called cations, while the negatively charged ions furnished by the electrolyte are called anions.
Types of Electrolytes
(a) Weak electrolytes: Electrolytes that are decomposable to a very small extent in their dilute solutions are called weak electrolytes. For example, organic acids, inorganic acids and bases etc.
(b) Strong electrolytes: Electrolytes that are highly decomposable in aqueous solution and conduct electricity frequently are called electrolytes. For example, mineral acid and salts of strong acid.
Electrode
For the electric current to pass through an electrolytic conductor, the two rods or plates called electrodes are always needed. These plates are connected to the terminals of the battery to form a cell. The electrode through which the electric current flows into the electrolytic solution is called the anode, also called the positive electrode, and anions are oxidised here.
An electrode through which the electric current flows out of the electrolytic solution is called the cathode, also called the negative electrode, and cations are reduced there.
Electrolysis
Electrolysis is the process of chemical deposition of the electrolyte by passing an electric current. Electrolysis takes place in an electrolytic cell. This cell will convert the electrical energy to chemical energy.
Class XII Electrochemistry - Nernst equation.Arunesh Gupta
Introduction, application of electrochemistry, metallic conduction & electrolytic conduction, electrolytes, electrochemical cell & electrolytic cell, Galvanic cell (Daniell cell), Standard reduction & oxidation potential, SHE as reference electrode, Standard emf of a cell or standard cell potential, Electrochemical series & its application, Nernst equation, Relationship between (i) Standard cell potential & equilibrium constant (ii) standard cell potential & standard Gibbs energy, some numerical problems.
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Notes and Important Points on Electrochemistry - JEE Main 2015
1. 1
Electrochemistry
Introduction
Electrochemistry is the branch of physical chemistry which deals with the relationship
between electrical energy and chemical changes taking place in redox reactions.
Electrolytes and Electrolysis
(1) Definition: “The substances whose aqueous solution undergos decomposition into
ions when electric current is passed through them are known as electrolytes and the
whole process is known as electrolysis or electrolytic decomposition.”
E.g.
Solutions of acids, bases, salts in water and fused salts etc. are the examples of
electrolytes. Electrolytes may be weak or strong. Solutions of cane sugar, glycerine,
alcohol etc., are examples of non-electrolytes.
(2) Electrolytic cell or Voltameter: The device in which the process of electrolysis or
electrolytic decomposition is carried out is known as electrolytic cell or voltameter.
(i) Voltameter converts electrical energy into chemical energy.
(ii) The electrode on which oxidation takes place is called anode (or +ve pole)
and the electrode on which reduction takes place is called cathode (or –ve
pole)
(iii) During electrolysis in voltameter cations are discharged on cathode and
anions on anode.
(iv) In voltameter, outside the electrolyte electrons flow from anode to cathode
and current flow from cathode to anode.
For voltameter, E cell = - ve and Δ G = + ve
(v) The anions on reaching the anode give up their electrons and converted into
the neutral atoms.
At anode: (Oxidation)
(vi) On the other hand cations on reaching the cathode take up electrons supplied
by battery and converted to the neutral atoms.
At cathode : (Reduction)
eAA–
BB
e
2. 2
This overall change is known as primary change and products formed is
known as primary products.
The primary products may be collected as such or they undergo further
change to form molecules or compounds. These are called secondary
products and the change is known as secondary change.
(3) Preferential discharge theory : According to this theory “If more than one type of ion
is attracted towards a particular electrode, then the ion is discharged one which
requires least energy or ions with lower discharge potential or which occur low in
the electrochemical series”.
The potential at which the ion is discharged or deposited on the appropriate
electrode is termed the discharge or deposition potential, (D.P.). The values of
discharge potential are different for different ions.
The decreasing order of discharge potential or the increasing order of
deposition of some of the ions is given below,
For cations:
For anions:
Products of electrolysis of some electrolytes
Electrolyte Electrode Product at cathode Product at anode
Aqueous NaOH Pt or Graphite 2H+ + 2e- →H2
Fused NaOH Pt or Graphite Na+ + e- → Na
Aqueous NaCl Pt or Graphite
Fused NaCl Pt or Graphite
Aqueous CuSO4 Pt or Graphite
Aqueous CuSO4 Cu electrode Cu oxidized to Cu2+
ions
Dilute H2SO4 Pt electrode
Conc. H2SO4 Pt electrode Peroxodisulphuric acid
H2S2O8
,,,,,,, 2322
ZnAlMgCaNaKLi ,2
Fe
.,,,,, 3222
AuAgHgCuHNi
.,,,,, 3
2
4
IBrClOHNOSO
2 2
1
2OH O H O 2e
2
2 2
1
2OH O H O 2e
2
22H 2e H
22Cl Cl 2e
Na e Na
22Cl Cl 2e
2
Cu 2e Cu
2 2
1
2OH O H O 2e
2
2
Cu 2e Cu
22H 2e H
2 2
1
2OH O H O 2e
2
22H 2e H
3. 3
Aqueous AgNO3 Pt electrode
Aqueous AgNO3 Ag electrode Ag oxidized to Ag+
ions
Ag e Ag
2 2
1
2OH O H O 2e
2
Ag e Ag
4. 4
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