55
Chapter 12
Electrochemistry
ASSIGNMENT
Single Choice Type Questions
1.
In which of the following aqueous solution, H2 is not produced at cathode if inert electrode is used during
electrolysis?
2.
(1) AgCl
(2) KCl
(3) AlCl3
(4) NaCl
The E.M.F. of cell at 25ºC is
Eo
Zn/ Zn2 +
3.
= 0.77 V
(1) –0.77 V
(2) 0.77 V
(3) 1.34 V
(4) 2.14 V
An electrochemical cell is given as
If the cell is spontaneous then X should be
4.
(1) 0.0001
(2) 0.001
(3) 0.002
(4) 0.02
Which of the following is correct statement?
(1) Electronic conductance decreases with increase in temperature
(2) Electronic conductance increase with increase in temperature
(3) Electronic conductance does not depend on the temperature
(4) Ionic conductance decreases with increase in temperature
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5.
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Consider the reaction :
Reaction I : Pb(s) + SO24− (aq) → PbSO 4 (s) + 2e −
Reaction II : PbO2 (s) + SO24 − (aq) + 4H+ → PbSO 4 (s) + 2H2O(s)
The correct statement is
(1) Reaction I takes place at cathode when battery is in use
(2) Reaction II takes place at cathode when battery is in use
(3) Reaction II takes place at anode when battery is in use
(4) Reaction I takes place at cathode during charging
6.
When 9.65 A current is passed for X minute in molten AgCl solution and 3.24 g of Ag is deposited at cathode.
The value of X is
7.
(1) 2
(2) 3
(3) 4
(4) 5
Consider the statements.
Statement I : Conductance of semiconductor increase with increase in temperature.
Statement II : Conductance of solid always increase with increase in temperature.
The correct statement(s)/are
8.
(1) Only I
(2) Only II
(3) Both I and II
(4) Neither I nor II
In which of the following solution, pH of solution will increase during electrolysis? (Assume electrode is inert)
(1) NaCl solution (aqueous) (concentrated)
(2) Molten NaCl solution
(3) Aqueous AgNO3 solution
(4) Aqueous Ag2SO4 solution
9.
o
EM/M
3 + values for M1, M2 and M3 are –0.5 V, 1.36 V, 0.76 V respectively. An aqueous solution containing the
tripositive ions is electrolysed. Which of the metal is most expected to be deposited at cathode under standard
conditions?
(1) M1
(2) M2
(3) M3
(4) M1, M2, M3 will be deposited in equal amounts
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10. Consider the  m (in S cm2 mol–1) values of the given species
NaCl = 126.4, HCl = 425.9, NaAc = 91 and KCl = 149.8. Then select the correct value of  m (in S cm2 mol–1)
of ion indicated if value of  m of Ac– is 40.9 S cm2 mol–1
(1) K+ : 73.5
(2) H+ : 359.6
(3) Cl– : 66.3
(4) Na+ : 60.1
11. Consider the  mo values given for the species (in S cm2 mol–1)
Na+ = 50.1
OH– = 199.1
Mg2+ = 106
Cl– = 76.3
To a 1 L solution of 0.1 M NaOH, 0.1 M MgCl2 is slowly added. Then select the correct statement out of the
following.
[Ksp Mg(OH)2 = 10–13 M3]
(1) The conductance of the solution increases with the addition of MgCl 2 and keeps on increasing
(2) The conductance of the solution decreases with the addition of MgCl2 and keeps on decreasing
(3) The conductance of the solution increases upto a certain amount of MgCl 2 added and then decreases
(4) The conductance of the solution decreases upto a certain amount of MgCl 2 added and then increases
12. Ksp of AgCl is 10–10 M2. If the values of  m , Ag+ = 54.3 Scm2 mol–1 and  m , Cl– = 65.5 S cm2 mol–1.
Then find the specific conductance (in S cm–1) of saturated solution of AgCl (Neglect conductivity of water)
(1) 2.4 × 10–11
(2) 2.4 × 10–8
(3) 1.2 × 10–8
(4) 1.2 × 10–6
13. An amalgam of cadmium is prepared by electrolysis of CdCl2 solution using mercury cathode. How long
(approx) should a current of 5 A be passed in order to prepare Cd-Hg amalgam containing 12.5% Cd(by
weight) on a cathode of 4 g Hg. (Molar mass of Cd = 113 g/mol)
(1) 193 s
(2) 96.5 s
(3) 386 s
(4) 482.5 s
14. A certain current liberates 0.5 g of H2 in 2 hour. The amount of copper deposited at the cathode during the
electrolysis Cu3(PO4)2 (aq) solution by consuming the same charge is (atomic mass of Cu = 63.5 amu)
(1) 15.875 g
(2) 63.5 g
(3) 31.75 g
(4) 190.5 g
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15. The resistance of a solution A is 50  solution B is 100  and that of solution C is 200  when all solutions
are taken in the same conductivity cell separately. If equal volume of all three solution are mixed. What will be
the resistance of the mixture using the same cell (Assume degree of dissociation of A, B & C does not changes
on mixing)?
(1) 80.1 
(2) 92.6 
(3) 85.7 
(4) 104.9 
16. By how much will the potential of half cell Cu+2/Cu change, if the solution is diluted to 100 times at 298 K?
(1) Increases by 59 mV
(2) Decreases by 59 mV
(3) Increases by 29.5 mV
(4) Decreases by 29.5 mV
17. The equilibrium constant for the reaction
Sr (s) + Mg+2 (aq)
Sr+2 (aq) + Mg (s) is 2.69 × 1012 at 25°C.
The E° for a cell made up of Sr/Sr+2 and Mg+2/Mg half cells is
(1) 0.3667 V
(2) 0.7346 V
(3) 0.1836 V
(4) 3.667 V
18. The specific conductance of a saturated solution of AgCl is K –1 cm–1. The limiting ionic conductances of Ag+
and Cl– are x and y, respectively. The solubility product of AgCl is
1000 K
(1)
x+y
(3)
1000  143.5  K
x+y
2
(2)
 1000 K 


 x+y 
(4)
 103  143.5  K 


x+y


2
19. Which of following type of plot would you expect from the titration of AgNO 3 against KCl solution?
(1)
(2)
(3)
(4)
20. Which is the correct order of deposition of anion?
(1) SO4–2 > OH– > Cl– > Br– > I–
(2) SO4–2 < OH– < CI– < Br– < I–
(3) SO4–2 > Cl– > Br– > I– > OH–
(4) Br– > Cl– > I– > SO4–2 > OH–
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Numerical Value Type Questions
21. The emf of a cell corresponding to the reaction
2Ag+ (0.1 M) + H2 (1 atm) ⎯⎯→ 2Ag(s) + 2H+ (Eo +
Ag / Ag
= 0.80 V)
is 1.04 V at 25ºC. Calculate the pH of the solution at the hydrogen electrode.
2.303 RT


= 0.06 
 Use
F


22. The conductivity of 0.001 M Na2SO4 solution is 2.6 × 10–4 S cm–1 and increases to 7.0 × 10–4 S cm–1 when the
solution is saturated with CaSO4. The molar conductivities of Na+ and Ca2+ ions are 50 and
120 S cm2 mol–1 respectively. By neglecting conductivity of water used, the solubility product of CaSO 4 is
y × 10–6. Find the value of 4y (To the nearest integer).
23. Find the cell potential of lead storage battery during discharging (in volt) at pH = 5 and 0.1 M SO42– at 25°C.
Given : Ecell = 1.97 V,
o
2.303 RT
= 0.06
F
24. Molar conductivity of 0.1 M CH3COOH at certain temperature is 256.62 S cm2 mol–1. What is its pH?
[ Ho + = 349.6 S cm2 mol–1,  oCH COO− = 78.1 S cm2 mol–1 and log(6) = 0.78]
3
25. AgBr(s)
Ag+(aq) + Br–(aq); E° = –0.72 V
If the value of Ksp at 25°C is 10–b then the value of b is (Use,
2.303 RT
= 0.06 )
F
26. For a cell, Cu(s) | Cu2+ (0.001M) || Ag+ (0.01M) | Ag(s) the cell potential is found to be 0.43 V at
298 K. The magnitude of standard electrode potential for Cu2+/Cu is ______ × 10–2 V.
2.303RT


Θ
= 0.06 V 
Given : EAg+ / Ag = 0.80 V and
F


27. Resistance of a conductivity cell (cell constant 129 m –1) filled with 74.5 ppm solution of KCI is 100  (labelled
as solution 1). When the same cell is filled with KCl solution of 149 ppm, the resistance is 50  (labelled as
solution 2). The ratio of molar conductivity of solution 1 and solution 2 is
1
= t  10–3 . The value of t is
2
_________. (Nearest integer)
(Given : molar mass of KCl is 74.5 g mol–1).
28. The cell potential for Zn|Zn2+(aq)||Snx+|Sn is 0.801 V at 298 K. The reaction quotient for the above reaction is
10–2. The number of electrons involved in the given electrochemical cell reaction is _____.
 Given : E 2 + = –0.763V, E x + = +0.008V 
Zn |Zn
Sn |Sn




2.303RT
and
= 0.06 V 


F

29. The cell potential for the given cell at 298 K
Pt | H2 (g, 1 bar) | H+ (aq) || Cu2+ (aq) | Cu(s)
is 0.31 V. The pH of the acidic solution is found to be 3, whereas the concentration of Cu2+ is 10–x M. The
value of x is _____.
= 0.34 V and
(Given: EΘ
Cu2 + /Cu
2.303 RT
= 0.06 V )
F
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30. A dilute solution of sulphuric acid is electrolysed using a current of 0.10 A for 2 hours to produce hydrogen and
oxygen gas. The total volume of gases produced at STP is ____ cm3. (Nearest integer)
[Given : Faraday constant F = 96500 C mol–1 at STP, molar volume of an ideal gas is 22.7 L mol–1]
31. Consider the following cell reaction
9
CdSO4  H2O(s) + 2Hg(l) .
5
9
Cd(s) + Hg2SO4(s) + H2O(l)
5
The value of Ecell is 4.315 V at 25°C. If Ho = –825.2 kJ mol–1, the standard entropy change So in J K–1 is
0
_______. (Nearest integer)
[Given : Faraday constant = 96487 C mol–1]
32. For the cell Cu(s) | Cu2+ (aq) (0.1 M) || Ag+ (aq) (0.01 M) | Ag(s) the cell potential E1 = 0.3095 V
For the cell Cu(s) | Cu2+ (aq) (0.01 M) || Ag+ (aq) (0.001 M) Ag(s) the cell potential = _____ × 10 –2 V. (Round
off to the Nearest Integer).
[Use :
2.303 RT
= 0.059 ]
F
33. Copper reduces NO3− into NO and NO2 depending upon the concentration of HNO 3 in solution. (Assuming
fixed [Cu2+] and PNO = PNO2 = 1 bar), the HNO3 concentration at which the thermodynamic tendency for
reduction of NO3− into NO and NO2 by copper is same is 10x M. The value of 2x is ______. (Rounded-off to
the nearest integer)


= 0.96 V, ENO
[Given, ECu2 + /Cu = 0.34 V, ENO
= 0.79 V and at 298 K,
−
−
/NO
/NO
3
3
2
RT
(2.303) = 0.059]
F
❑ ❑ ❑
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