CBSE Class-12 Chemistry Quick Revision Notes
Chapter-03: Electrochemistry
• Oxidation:
It is defined as a loss of electrons while reduction is defined as a gain of electrons.
• In a redox reaction, both oxidation and reduction reaction takes place simultaneously.
• Direct redox reaction:
In a direct redox reaction, both oxidation and reduction reactions take place in the same
vessel. Chemical energy is converted to heat energy in a direct redox reaction.
• Indirect redox reaction:
In indirect redox reactions, oxidation and reduction take place in different vessels.
• In an indirect redox reaction, chemical energy is converted into electrical energy. The
device which converts chemical energy into electrical energy is known as an
electrochemical cell.
• In an electrochemical cell:
a) The half-cell in which oxidation takes place is known as oxidation half-cell
b) The half-cell in which reduction takes place is known as reduction half-cell.
c) Oxidation takes place at anode which is negatively charged and reduction takes
place at cathode which is positively charged.
d) Transfer of electrons takes place from anode to cathode while electric current
flows in the opposite direction.
e) An electrode is made by dipping the metal plate into the electrolytic solution of its
soluble salt.
f) A salt bridge is a U shaped tube containing an inert electrolyte in agar-agar and
gelatine.
• Salt bridge:
A salt bridge maintains electrical neutrality and allows the flow of electric current by
completing the electrical circuit.
• Representation of an electrochemical cell:
a) Anode is written on the left while the cathode is written on the right.
b) Anode represents the oxidation half-cell and is written as:
Metal/Metal ion (Concentration)
c) Cathode represents the reduction half-cell and is written as:
Metal ion (Concentration)/Metal
d) Salt bridge is indicated by placing double vertical lines between the anode and
the cathode
e) Electrode potential is the potential difference that develops between the
electrode and its electrolyte. The separation of charges at the equilibrium state
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, results in the potential difference between the metal and the solution of its ions. It
is the measure of tendency of an electrode in the half cell to lose or gain electrons.
• Standard electrode potential:
When the concentration of all the species involved in a half cell is unity, then the
electrode potential is known as standard electrode potential. It is denoted as EΘ.
• According to the present convention, standard reduction potentials are now called
standard electrode potential.
• Types of electrode potential:
There are 2 types of electrode potentials namely,
a) Oxidation potential
b) Reduction potential
• Oxidation potential:
It is the tendency of an electrode to lose electrons or get oxidized.
• Reduction potential:
It is the tendency of an electrode to gain electrons or get reduced.
• Oxidation potential is the reverse of reduction potential.
• The electrode having a higher reduction potential have higher tendency to gain electrons
and so it acts as a cathode whereas the electrode having a lower reduction potential acts
as an anode.
• The standard electrode potential of an electrode cannot be measured in isolation.
• According to convention, the Standard Hydrogen Electrode is taken as a reference
electrode and it is assigned a zero potential at all temperatures.
• Reference electrode:
Standard calomel electrode can also be used as a reference electrode.
• SHE:
Standard hydrogen electrode consists of a platinum wire sealed in a glass tube and
carrying a platinum foil at one end. The electrode is placed in a beaker containing an
aqueous solution of an acid having 1 Molar concentration of hydrogen ions. Hydrogen
gas at 1 bar pressure is continuously bubbled through the solution at 298 K. The
oxidation or reduction takes place at the Platinum foil. The standard hydrogen electrode
can act as both anode and cathode.
• If the standard hydrogen electrode acts as an anode:
H 2 ( g ) → 2 H + ( aq ) + 2e −
• If the standard hydrogen electrode acts as a cathode:
2 H + (aq ) + 2e → H 2 ( g )
• In the electrochemical series, various elements are arranged as per their standard
reduction potential values.
• A substance with higher reduction potential value means that it has a higher tendency to
get reduced. So, it acts as a good oxidising agent.
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Chapter-03: Electrochemistry
• Oxidation:
It is defined as a loss of electrons while reduction is defined as a gain of electrons.
• In a redox reaction, both oxidation and reduction reaction takes place simultaneously.
• Direct redox reaction:
In a direct redox reaction, both oxidation and reduction reactions take place in the same
vessel. Chemical energy is converted to heat energy in a direct redox reaction.
• Indirect redox reaction:
In indirect redox reactions, oxidation and reduction take place in different vessels.
• In an indirect redox reaction, chemical energy is converted into electrical energy. The
device which converts chemical energy into electrical energy is known as an
electrochemical cell.
• In an electrochemical cell:
a) The half-cell in which oxidation takes place is known as oxidation half-cell
b) The half-cell in which reduction takes place is known as reduction half-cell.
c) Oxidation takes place at anode which is negatively charged and reduction takes
place at cathode which is positively charged.
d) Transfer of electrons takes place from anode to cathode while electric current
flows in the opposite direction.
e) An electrode is made by dipping the metal plate into the electrolytic solution of its
soluble salt.
f) A salt bridge is a U shaped tube containing an inert electrolyte in agar-agar and
gelatine.
• Salt bridge:
A salt bridge maintains electrical neutrality and allows the flow of electric current by
completing the electrical circuit.
• Representation of an electrochemical cell:
a) Anode is written on the left while the cathode is written on the right.
b) Anode represents the oxidation half-cell and is written as:
Metal/Metal ion (Concentration)
c) Cathode represents the reduction half-cell and is written as:
Metal ion (Concentration)/Metal
d) Salt bridge is indicated by placing double vertical lines between the anode and
the cathode
e) Electrode potential is the potential difference that develops between the
electrode and its electrolyte. The separation of charges at the equilibrium state
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, results in the potential difference between the metal and the solution of its ions. It
is the measure of tendency of an electrode in the half cell to lose or gain electrons.
• Standard electrode potential:
When the concentration of all the species involved in a half cell is unity, then the
electrode potential is known as standard electrode potential. It is denoted as EΘ.
• According to the present convention, standard reduction potentials are now called
standard electrode potential.
• Types of electrode potential:
There are 2 types of electrode potentials namely,
a) Oxidation potential
b) Reduction potential
• Oxidation potential:
It is the tendency of an electrode to lose electrons or get oxidized.
• Reduction potential:
It is the tendency of an electrode to gain electrons or get reduced.
• Oxidation potential is the reverse of reduction potential.
• The electrode having a higher reduction potential have higher tendency to gain electrons
and so it acts as a cathode whereas the electrode having a lower reduction potential acts
as an anode.
• The standard electrode potential of an electrode cannot be measured in isolation.
• According to convention, the Standard Hydrogen Electrode is taken as a reference
electrode and it is assigned a zero potential at all temperatures.
• Reference electrode:
Standard calomel electrode can also be used as a reference electrode.
• SHE:
Standard hydrogen electrode consists of a platinum wire sealed in a glass tube and
carrying a platinum foil at one end. The electrode is placed in a beaker containing an
aqueous solution of an acid having 1 Molar concentration of hydrogen ions. Hydrogen
gas at 1 bar pressure is continuously bubbled through the solution at 298 K. The
oxidation or reduction takes place at the Platinum foil. The standard hydrogen electrode
can act as both anode and cathode.
• If the standard hydrogen electrode acts as an anode:
H 2 ( g ) → 2 H + ( aq ) + 2e −
• If the standard hydrogen electrode acts as a cathode:
2 H + (aq ) + 2e → H 2 ( g )
• In the electrochemical series, various elements are arranged as per their standard
reduction potential values.
• A substance with higher reduction potential value means that it has a higher tendency to
get reduced. So, it acts as a good oxidising agent.
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