1
Unit 3. ELECTROCHEMISTRY-II
Galvanic cell, electrode potential, Nernst equation, derivation, cell representation and cell reaction.
Standard cell –Weston cadmium cell. Types of electrodes (details), construction of glass electrode,
reference electrode – calomel electrode. Determination of pH using quinhydrone, glass
electrodes.Concentration cells-types and application (solubility of sparingly soluble salts),
potentiometric titrations –principle and advantages, acid base titration. Fuel cells-types, working of
methanol-oxygen andproton exchange membrane fuel cells. Solar cells-Construction and working.
6 hrs
Electrochemistry is a branch of physical chemistry dealing with interconversion of chemical energy
and electrical energy.
Electrochemical cells: A device for producing electric current from a redox reaction.
(It is an assembly of two electrodes in a suitable electrolyte)
(i) Converts electrical energy to chemical energy
(ii) Converts chemical energy to electrical energy
Electrochemical cells
Electrolytic Galvanic (Voltaic)
Current passed through the cell to bring chemical reaction or physical
about the chemical change change will produce current
Chemical cell Concentration cell
Emf due to chemical reaction emf due to free energy decrease due
to difference in the conc.
Primary cell Secondary cell Fuel cell
Dry cell Alkaline battery Methanol – oxygen fuel cell
Can a redox reaction generate current?
When a redox reaction happens together it cannot generate current. But when the same reaction is
separated into two half reactions (oxidation in separate container and reduction in separate container)
and connected with a wire, it can generate current but it stops instantly as charge gets built up. In the
same set up if a salt bridge is kept through which ions move from one electrolyte to another, then a
continuous current flows.
Single electrode potential
The potential established at the metal and its solution interface is a measure of the tendency of the
metal to lose or gain electrons, which is referred to as single electrode potential.
, 2
Galvanic cell or voltaic cell
A Voltaic cell (Galvanic cell) is one in which electric
current is generated by a spontaneous reaction.
A bar of zinc metal (anode) is placed in ZnSO4 solution,
and a bar of copper metal is placed in CuSO4 solution.
The zinc and copper electrodes are connected by a copper
wire. A salt bridge containing potassium chloride solution
connects the two solutions. The oxidation half reaction
occurs at the Zn half-cell and the reduction half reaction
takes place at the Cu half-cell.
When the cell is set up, electrons flow from Zn to Cu
electrode and ions move from cathode to anode, which
complete the circuit thereby ensuring a continuous
supply of current. The cell will operate till either the Zn
metal or Copper ions are completely used up.
i.e., Galvanic cell has two electrodes separated by a porous partition or a salt bridge. Oxidation occurs
at one cell and reduction at other.
Anode: M → Mn+ + ne− (Oxidation) Cathode: Mn+ + ne− → M (Reduction)
Electrode and its solution in a voltaic cell is called a half cell.
Sign Convention
• The anode is where oxidation occurs, and the cathode is the site of reduction. In an actual cell, the
identity of the electrodes depends on the direction in which the net cell reaction is occurring.
• If electrons flow from the left electrode to the right electrode (as depicted in the above cell notation)
when the cell operates in its spontaneous direction, the potential of the right electrode will be
higher than that of the left, and the cell potential will be positive.
• "Conventional current flow" is from positive to negative, which is opposite to the direction of the
electron flow. This means that if the electrons are flowing from the left electrode to the right, a
galvanometer placed in the external circuit would indicate a current flow from right to left.
EMF: Electromotive force/ cell potential
Definition: The potential developed on the metal surface at equilibrium. (or) The difference in the
potential which causes a current to flow from electrode of higher potential to that of lower potential is
called emf of the cell.
Ecell = E(cathode) – E(anode)
= ERHE – ELHE
It is expressed in volts.
The absolute value of the reduction potential ERHE & ELHE cannot be determined. These are found by
connecting the half cell with a SHE, whose reduction potential is fixed as zero.
Standard electrode potential
If in the half cell, the metal rod is suspended in a solution of one molar concentration, the temperature
is kept at 298 K, the electrode potential is called standard electrode potential (Eo)
Cell representation
Anode (−) Before Cathode (+)
Oxdn. Redn.
Single line: Phase difference
Double line: Salt bridge
Unit 3. ELECTROCHEMISTRY-II
Galvanic cell, electrode potential, Nernst equation, derivation, cell representation and cell reaction.
Standard cell –Weston cadmium cell. Types of electrodes (details), construction of glass electrode,
reference electrode – calomel electrode. Determination of pH using quinhydrone, glass
electrodes.Concentration cells-types and application (solubility of sparingly soluble salts),
potentiometric titrations –principle and advantages, acid base titration. Fuel cells-types, working of
methanol-oxygen andproton exchange membrane fuel cells. Solar cells-Construction and working.
6 hrs
Electrochemistry is a branch of physical chemistry dealing with interconversion of chemical energy
and electrical energy.
Electrochemical cells: A device for producing electric current from a redox reaction.
(It is an assembly of two electrodes in a suitable electrolyte)
(i) Converts electrical energy to chemical energy
(ii) Converts chemical energy to electrical energy
Electrochemical cells
Electrolytic Galvanic (Voltaic)
Current passed through the cell to bring chemical reaction or physical
about the chemical change change will produce current
Chemical cell Concentration cell
Emf due to chemical reaction emf due to free energy decrease due
to difference in the conc.
Primary cell Secondary cell Fuel cell
Dry cell Alkaline battery Methanol – oxygen fuel cell
Can a redox reaction generate current?
When a redox reaction happens together it cannot generate current. But when the same reaction is
separated into two half reactions (oxidation in separate container and reduction in separate container)
and connected with a wire, it can generate current but it stops instantly as charge gets built up. In the
same set up if a salt bridge is kept through which ions move from one electrolyte to another, then a
continuous current flows.
Single electrode potential
The potential established at the metal and its solution interface is a measure of the tendency of the
metal to lose or gain electrons, which is referred to as single electrode potential.
, 2
Galvanic cell or voltaic cell
A Voltaic cell (Galvanic cell) is one in which electric
current is generated by a spontaneous reaction.
A bar of zinc metal (anode) is placed in ZnSO4 solution,
and a bar of copper metal is placed in CuSO4 solution.
The zinc and copper electrodes are connected by a copper
wire. A salt bridge containing potassium chloride solution
connects the two solutions. The oxidation half reaction
occurs at the Zn half-cell and the reduction half reaction
takes place at the Cu half-cell.
When the cell is set up, electrons flow from Zn to Cu
electrode and ions move from cathode to anode, which
complete the circuit thereby ensuring a continuous
supply of current. The cell will operate till either the Zn
metal or Copper ions are completely used up.
i.e., Galvanic cell has two electrodes separated by a porous partition or a salt bridge. Oxidation occurs
at one cell and reduction at other.
Anode: M → Mn+ + ne− (Oxidation) Cathode: Mn+ + ne− → M (Reduction)
Electrode and its solution in a voltaic cell is called a half cell.
Sign Convention
• The anode is where oxidation occurs, and the cathode is the site of reduction. In an actual cell, the
identity of the electrodes depends on the direction in which the net cell reaction is occurring.
• If electrons flow from the left electrode to the right electrode (as depicted in the above cell notation)
when the cell operates in its spontaneous direction, the potential of the right electrode will be
higher than that of the left, and the cell potential will be positive.
• "Conventional current flow" is from positive to negative, which is opposite to the direction of the
electron flow. This means that if the electrons are flowing from the left electrode to the right, a
galvanometer placed in the external circuit would indicate a current flow from right to left.
EMF: Electromotive force/ cell potential
Definition: The potential developed on the metal surface at equilibrium. (or) The difference in the
potential which causes a current to flow from electrode of higher potential to that of lower potential is
called emf of the cell.
Ecell = E(cathode) – E(anode)
= ERHE – ELHE
It is expressed in volts.
The absolute value of the reduction potential ERHE & ELHE cannot be determined. These are found by
connecting the half cell with a SHE, whose reduction potential is fixed as zero.
Standard electrode potential
If in the half cell, the metal rod is suspended in a solution of one molar concentration, the temperature
is kept at 298 K, the electrode potential is called standard electrode potential (Eo)
Cell representation
Anode (−) Before Cathode (+)
Oxdn. Redn.
Single line: Phase difference
Double line: Salt bridge
