UNIT-II ELECTROCHEMISTRY 9
Terminology involved in electrochemistry – Types of Cells - Galvanic and concentration cells-
Derivation of Nernst equation - Applications of Electrochemical series - Types of Electrodes -
Hydrogen, Calomel, ion-selective electrode - Determination of pH using glass electrode -
Determination of electrode potentials - Conductometric titrations - Potentiometric titration-Redox
titration.
2.0 Electrochemistry is the branch of science which deals with the relationship between
Chemical energy and electrical energy and the interconversion of one form into other.
i.e., Chemical reactions produced by passing electric current through an electrolyte or
production of electric curerent through a chemical reaction
2.1 Terminology involved in electrochemistry
Conductors: Conductors are substances which allow electricity to pass through them.
Examples: All metals, graphite, fused salts, solution of electrolytes.
Non-conductors (Insulators): Substances which do not allow the passage of electric current
through them are called non-conductors.Examples: wood, plastics, rubber, most of non metals
Types of conductors
(i) Metallic conductors : Metallic conductors allow electricity to pass
through them without undergoing any chemical change. The flow of electric
current is due to the f low of electron in the metal.
(ii) Electrolytic conductors : These are substances which allow electricity to
pass through them in their molten states or in their aqueous solutions. Conduction
occurs due to the movement of ions
Differences between metallic conduction and electrolytic conduction
Metallic conduction Electrolytic conduction
Conduction occurs due to the Conduction occurs due to the
movement of electrons movement of ions in a solution
Does not involve any transfer Involves transfer of electrolyte
of matter in the form of ions
Conduction decreases with Conduction increases with
1
,Types of electrolytic conductors
Strong electrolytes: Completely dissociate into ions in solution
Examples: HCl, NaOH, NaCl, KCl
Weak electrolytes: Which dissociate only to some extent insolution
Non – electrolytes: Do not ionise in solution
Cell Terminology
i. Current : Flow of electrons through a conductor
ii. Electrode : Electrode is a material (rod, bar, strip)which conducts
electrons
iii. Anode : Electrode at which oxidation occurs
iv. Cathode : Electrode at which reduction occurs
v. Electrolyte : Water soluble substance forming ions in solution and
conducts electric current
vi. Anode compartment: Compartment of the cell in which the oxidation
half reaction occurs. Contains the anode
vii. Cathode compartment: Compartment of the cell in which the
reduction half reaction occurs. Contains the cathode
viii. Half – cell: Part of the cell, which contains an electrolyte dipped in an
electrolyte. If oxidation occurs in this half, then it is called the oxidation
halfcell. If reduction occurs at the cell, it is called the reduction half
cell
ix. Cell: Device consisting of two halfcell. The two half cells are connected
by a conductor
Standard electrode potential
The electrode potential developed when the concentration of the solution is 1 molar,
temperature 25C and pressure 1 atmosphere (if gaseous electrode), is called standard electrode
potential (Eo); These values are available for various system in EMF series. It is also known as
half cell potential.
2
, Single electrode potential
When a metal is placed in a solution of it’s salt, a potential is developed between the
metal and the solution because of the formation of a double layer. It is known as single electrode
potential. It is the measure of tendency of the metal to loose or gain electrons. It may be
oxidation potential (Eox) or reduction potential (ER). The value of it may be either +ve or –ve.
The electrode potential depends on the concentration, temperature, and pH of the
solution. It is measured in volt.
Types of electrode
i) Gas electrode. Example : Hydrogen electrode H+ ½ H2
ii) Metal – metal ion electrode. Example : Zinc electrode Zn / Zn2+ or ZnSO4
iii) Metal – metal insoluble salt electrode.
Example : Calomel electrode. Hg – Hg2Cl2, KCl Pt
iv) Redox electrode. Example : Quine – hydrone electrode.
v) Ion selective electrode. Example : Glass electrode.
Reference electrodes
The electrode potential of some electrodes is known and their values do not vary for a
long time. Other electrodes may be coupled with them to find out their single electrode
potentials. They are called reference electrodes.
(i) Primary reference electrode - Standard Hydrogen Electrode (SHE)
(ii) Secondary reference electrode - Calomel electrode, glass electrode, quinhydrone electrode
i) Hydrogen electrode : It is primary reference electrode. It’s single electrode potential is fixed
zero.
ii) Calomel electrode : It is secondary or subsidary reference electrode. The saturated calomel
electrode has the fixed electrode potential Eo =0.2422 V.
SCE
Indicator electrodes
Indicator electrodes are those which are sensitive to a particular type of ions. Their
potentials are also variable with the concentration of such ions.
Example : Glass electrode – sensitive hydrogen ion. Inert metals Pt, Ag electrodes
3
Terminology involved in electrochemistry – Types of Cells - Galvanic and concentration cells-
Derivation of Nernst equation - Applications of Electrochemical series - Types of Electrodes -
Hydrogen, Calomel, ion-selective electrode - Determination of pH using glass electrode -
Determination of electrode potentials - Conductometric titrations - Potentiometric titration-Redox
titration.
2.0 Electrochemistry is the branch of science which deals with the relationship between
Chemical energy and electrical energy and the interconversion of one form into other.
i.e., Chemical reactions produced by passing electric current through an electrolyte or
production of electric curerent through a chemical reaction
2.1 Terminology involved in electrochemistry
Conductors: Conductors are substances which allow electricity to pass through them.
Examples: All metals, graphite, fused salts, solution of electrolytes.
Non-conductors (Insulators): Substances which do not allow the passage of electric current
through them are called non-conductors.Examples: wood, plastics, rubber, most of non metals
Types of conductors
(i) Metallic conductors : Metallic conductors allow electricity to pass
through them without undergoing any chemical change. The flow of electric
current is due to the f low of electron in the metal.
(ii) Electrolytic conductors : These are substances which allow electricity to
pass through them in their molten states or in their aqueous solutions. Conduction
occurs due to the movement of ions
Differences between metallic conduction and electrolytic conduction
Metallic conduction Electrolytic conduction
Conduction occurs due to the Conduction occurs due to the
movement of electrons movement of ions in a solution
Does not involve any transfer Involves transfer of electrolyte
of matter in the form of ions
Conduction decreases with Conduction increases with
1
,Types of electrolytic conductors
Strong electrolytes: Completely dissociate into ions in solution
Examples: HCl, NaOH, NaCl, KCl
Weak electrolytes: Which dissociate only to some extent insolution
Non – electrolytes: Do not ionise in solution
Cell Terminology
i. Current : Flow of electrons through a conductor
ii. Electrode : Electrode is a material (rod, bar, strip)which conducts
electrons
iii. Anode : Electrode at which oxidation occurs
iv. Cathode : Electrode at which reduction occurs
v. Electrolyte : Water soluble substance forming ions in solution and
conducts electric current
vi. Anode compartment: Compartment of the cell in which the oxidation
half reaction occurs. Contains the anode
vii. Cathode compartment: Compartment of the cell in which the
reduction half reaction occurs. Contains the cathode
viii. Half – cell: Part of the cell, which contains an electrolyte dipped in an
electrolyte. If oxidation occurs in this half, then it is called the oxidation
halfcell. If reduction occurs at the cell, it is called the reduction half
cell
ix. Cell: Device consisting of two halfcell. The two half cells are connected
by a conductor
Standard electrode potential
The electrode potential developed when the concentration of the solution is 1 molar,
temperature 25C and pressure 1 atmosphere (if gaseous electrode), is called standard electrode
potential (Eo); These values are available for various system in EMF series. It is also known as
half cell potential.
2
, Single electrode potential
When a metal is placed in a solution of it’s salt, a potential is developed between the
metal and the solution because of the formation of a double layer. It is known as single electrode
potential. It is the measure of tendency of the metal to loose or gain electrons. It may be
oxidation potential (Eox) or reduction potential (ER). The value of it may be either +ve or –ve.
The electrode potential depends on the concentration, temperature, and pH of the
solution. It is measured in volt.
Types of electrode
i) Gas electrode. Example : Hydrogen electrode H+ ½ H2
ii) Metal – metal ion electrode. Example : Zinc electrode Zn / Zn2+ or ZnSO4
iii) Metal – metal insoluble salt electrode.
Example : Calomel electrode. Hg – Hg2Cl2, KCl Pt
iv) Redox electrode. Example : Quine – hydrone electrode.
v) Ion selective electrode. Example : Glass electrode.
Reference electrodes
The electrode potential of some electrodes is known and their values do not vary for a
long time. Other electrodes may be coupled with them to find out their single electrode
potentials. They are called reference electrodes.
(i) Primary reference electrode - Standard Hydrogen Electrode (SHE)
(ii) Secondary reference electrode - Calomel electrode, glass electrode, quinhydrone electrode
i) Hydrogen electrode : It is primary reference electrode. It’s single electrode potential is fixed
zero.
ii) Calomel electrode : It is secondary or subsidary reference electrode. The saturated calomel
electrode has the fixed electrode potential Eo =0.2422 V.
SCE
Indicator electrodes
Indicator electrodes are those which are sensitive to a particular type of ions. Their
potentials are also variable with the concentration of such ions.
Example : Glass electrode – sensitive hydrogen ion. Inert metals Pt, Ag electrodes
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