Unit -3 – Electrochemistry
Section A:
I] Multiple Choice Questions:
1.
2.
3.
4.
5.
The emf of the cell:
Ni / Ni2+ (1.0 M) // Au3+ (1.0 M) / Au (E° = -0.25 V for Ni2+/Ni; E° = 1.5 V for Au3+/Au) is
(a) 1.25 V
(b) -1.25 V
(c) 1.75 V
(d) 2.0 V
The difference between electrode potentials of two electrodes when no current is drawn
through the cell is ___________________
(a) cell potential
(b) EMF
(c) potential difference
(d) Cell voltage
Fused NaCl on electrolysis gives ………….. on cathode.
(a) Chlorine
(b) Sodium
(c) Sodium amalgam
(d) Hydrogen
An electrochemical cell can behave like an electrolytic cell when
(a) Ecell = 0 (b) Ecell > E ext (c) Eext > E cell (d) Ecell = E ext
The standard electrode potentials for the half cell reactions are:
Zn → Zn2-– 2e– E° = 0.76 V
Fe → Fe2- + 2– E° = -0.41 V
The emf of the cell reaction
Fe2- + Zn → Zn2- + Fe is
(a) -0.35 V
(b) +0.35 V
(c) -1.17 V
(d) +1.17 V
II] Read the given passage and answer the questions based on passage and related concepts studied
The conductivity or specific conductivity of an electrolytic solution varies with the concentration of
the solutions of different electrolytes. For comparing the conductances of the solutions of different
electrolytes, it is essential that the solutions should have equal volumes and they must contain
definite amount of the electrolytes which give ions carrying the same total charge. The conducting
power of an electrolytic solution can be expressed in terms of equivalent conductance and molar
conductance. The equivalent conductance of a solution does not vary linearly with concentration and
it is related with specific conductance. The effect of equivalent conductance can be studied by
plotting values against the square root of the concentration. Following two figures show the
behaviour of strong and weak electrolytes with change of concentration.
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The following questions are multiple choice questions. Choose the most appropriate answer:
6.
7.
8.
9.
Write the relationship between specific conductivity and equivalent conductivity?
What is the effect of decreasing concentration on the molar conductivity of a weak electrolyte?
Write the mathematical expression for Kohlrausch’s law in terms of equivalent conductivities.
What is meant by limiting molar conductivity?
III] Assertion-reason questions:
In the following questions, a statement of assertion followed by a statement of reason is given.
Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is the correct explanation for
assertion.
(b) Assertion and reason both are correct statements and reason is not the correct explanation for
assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.
10. Assertion
Reason
11. Assertion
Reason
12. Assertion
Reason
13. Assertion
Reason
14. Assertion
Reason
: More negative the electrode potential greater is the power to
act as oxidising agent.
: As the electrode potential becomes more negative there is
greater tendency to undergo oxidation
: E Ag +/Ag increases with increase in concentration of Ag+ ions.
: E Ag +/Ag has a positive value.
: For measuring resistance of an ionic solution, AC source is used.
: Concentration of ionic solution will change if DC source is used.
: Current stops flowing when Ecell = 0
: Equilibrium of the cell reaction is attained.
: Mercury cell does not give steady potential.
: In the cell reaction, ions are not involved in solution.
Section B:
III] Answer the following:
15. Define specific resistance.
16. Represent the galvanic cell in which the reaction ,
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) takes place
17. Express the relation among the cell constant, the resistance of the solution in the cell and the
conductivity of the solution. How is the conductivity of a solution related to its
molar conductivity?
18. The conductivity of 0.20 M solution of KCl at 298 K is 0.025Scm-1. Calculate its molar
conductivity.
19. Predict the products of electrolysis of the following:
i) An aqueous solution of sodium chloride with platinum electrodes
ii) A dilute solution of sulphuric acid with platinum electrodes
20. The conductivity of 0.001 M acetic acid is 4 × 10-5 S/cm. Calculate the dissociation constant
of acetic acid, if molar conductivity at infinite dilution for acetic acid is 390 S cm2/mol.
…………………………………………………….
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