ELECTROCHEMISTRY (04 MARKS)
Electrochemical Cell / Daniel cell
When Eext<1.1 V
When Eext=1.1 V
When Eext>1.1 V
,**electrode potential : A potential difference develops between the electrode and the
electrolyte .
**standard electrode potential : When the concentrations of all the species involved in a half-
cell is unity .
Cell potential : The potential difference between the two electrodes of a galvanic cell and is
measured in volts.
The cell potential is the difference between the electrode potentials (reduction potentials) of
the cathode and anode.
electromotive force (emf) : of the cell when no current is drawn through the cell.
Representation of Galvanic cell :
A galvanic cell represented by putting a vertical line between metal and electrolyte solution
and putting a double vertical line between the two electrolytes connected by a salt bridge.
Zn (s) / Zn2+ (aq) ⎥⎥ Cu2+ (aq) / Cu (s)
Cu(s) + 2Ag+(aq) ⎯→ Cu2+ (aq) + 2 Ag(s)
E cell = E cathode – E anode
Ecell = E right – E left
Half-cell reactions:
2+
Anode (oxidation): Cu(s) → Cu (aq) + 2e–
+
Cathode (reduction): 2Ag (aq) + 2e– → 2Ag(s)
2+ +
cell can be represented as Cu (s) | Cu (aq) || Ag (aq) | Ag (s)
Ecell = Eright –Eleft
=E Ag+/Ag – E Cu2+/Cu
Measurement of Electrode Potential :
The potential of individual half-cell cannot be measured. We can measure only the difference
between the two half-cell potentials that gives the emf of the cell. If we arbitrarily choose the
potential of one electrode (half-cell) then that of the other can be determined with respect to
this.
According to convention, a half-cell called standard hydrogen electrode represented by Pt (s)⎥
H2(g)/ H+ (aq) , is assigned a zero potential at all temperatures corresponding to the reaction.
, Sometimes metals like platinum or gold are used as inert electrodes.
They do not participate in the reaction but provide their surface for oxidation or reduction
reactions and for the conduction of electrons.
For example, Pt is used in the following half-cells:
Questions
3.1 How would you determine the standard electrode potential of the system Mg2+ | Mg?
3.2 Can you store copper sulphate solutions in a zinc pot?
3.3 Consult the table of standard electrode potentials and suggest three substances that can
oxidise ferrous ions under suitable conditions.
Electrochemical Cell / Daniel cell
When Eext<1.1 V
When Eext=1.1 V
When Eext>1.1 V
,**electrode potential : A potential difference develops between the electrode and the
electrolyte .
**standard electrode potential : When the concentrations of all the species involved in a half-
cell is unity .
Cell potential : The potential difference between the two electrodes of a galvanic cell and is
measured in volts.
The cell potential is the difference between the electrode potentials (reduction potentials) of
the cathode and anode.
electromotive force (emf) : of the cell when no current is drawn through the cell.
Representation of Galvanic cell :
A galvanic cell represented by putting a vertical line between metal and electrolyte solution
and putting a double vertical line between the two electrolytes connected by a salt bridge.
Zn (s) / Zn2+ (aq) ⎥⎥ Cu2+ (aq) / Cu (s)
Cu(s) + 2Ag+(aq) ⎯→ Cu2+ (aq) + 2 Ag(s)
E cell = E cathode – E anode
Ecell = E right – E left
Half-cell reactions:
2+
Anode (oxidation): Cu(s) → Cu (aq) + 2e–
+
Cathode (reduction): 2Ag (aq) + 2e– → 2Ag(s)
2+ +
cell can be represented as Cu (s) | Cu (aq) || Ag (aq) | Ag (s)
Ecell = Eright –Eleft
=E Ag+/Ag – E Cu2+/Cu
Measurement of Electrode Potential :
The potential of individual half-cell cannot be measured. We can measure only the difference
between the two half-cell potentials that gives the emf of the cell. If we arbitrarily choose the
potential of one electrode (half-cell) then that of the other can be determined with respect to
this.
According to convention, a half-cell called standard hydrogen electrode represented by Pt (s)⎥
H2(g)/ H+ (aq) , is assigned a zero potential at all temperatures corresponding to the reaction.
, Sometimes metals like platinum or gold are used as inert electrodes.
They do not participate in the reaction but provide their surface for oxidation or reduction
reactions and for the conduction of electrons.
For example, Pt is used in the following half-cells:
Questions
3.1 How would you determine the standard electrode potential of the system Mg2+ | Mg?
3.2 Can you store copper sulphate solutions in a zinc pot?
3.3 Consult the table of standard electrode potentials and suggest three substances that can
oxidise ferrous ions under suitable conditions.
