CHAPTER PRACTICE PROBLEMS
FIITJEE
CHEMISTRY
Electrochemistry
Name: ______________________________________ Batch:
Date:
Electrolytic Cells
1. It is not advisable to
(A) stir sugar solution with a silver spoon
(C) stir copper sulphate solution with a zinc spoon
2.
(B) stir copper sulphate solution with a silver spoon
(D) stir copper nitrate solution with a silver spoon.
[Ans: C]
M 2+ → M, 0.275g of metal M is deposited at the cathode due to passage of 1A of current for 956 sec. The
atomic weight of metal M is
(A) 27.5
(B) 55
(C) 110
(D) 13.75
[Ans : B]
3. During electrolysis of acidified water, O2 gas is formed at anode. To produce O2 at anode at the rate of 0.224
ml per second at STP, current passed is
(A) 0.224 A
(B) 2.24 A
(C) 9.65 A
(D) 3.86 A
[Ans : D]
4. Same quantity of current is passed through molten NaCl and molten cryolite containing Al2O3. If 4.6 g of
sodium were liberated in one cell, the mass of Al deposited in other cell was
(A) 0.9 g
(B) 2.7 g
(C) 1.8 g
(D) 3.6 g
[Ans : C]
5. 1 mol of electrons passes through each of the solution of AgNO3, CuSO4 and AlCl3. The molar ratio of Ag, Cu
& Al deposited is
(A) 1: 1: 1
(B) 6 : 3 : 2
(C) 6 : 3 : 1
(D) 1: 3 : 6
[Ans : B]
6. An aqueous solution of Na2SO4 was electrolyzed for 30 min; 25 mL of O2 was produced at the anode over
0
water at 22 C at a total pressure of 722 torr. Determine the strength of current that was used to produce the
0
oxygen gas. Vapour pressure of water at 22 C is 19.83 torr.
7. A piece of copper metal is to be electroplated on all side with silver to a thickness of 1 micrometer. If the
metal strip measures 50 mm × 10 mm × 1 mm, how long must the solution, which consists the Ag(CN)2 ion,
be electrolyzed, using a current of 100 mA? The density of silver metal is 10.5 g/cc.
8. 19 g of fused SnCl2 was electrolyzed using inert electrode when 0.119 g of Sn was deposited at cathode. If
nothing was given out during electrolysis, calculate the ratio of weight of SnCl2 and SnCl4 in fused state after
electrolysis.
+
+
+
9. A solution is 0.1 M in Au ions and 0.1 M in Ag ions. The standard reduction potential of Au is 1.68 V, while
-39
the dissociation constant of Au(CN)2 is 5 × 10 . What concentration of NaCN will have to be maintained in
0
the given solution in order to deposit Au and Ag simultaneously? [E Ag+/Ag = 0.8 V]
10. A test for complete removal of Cu
2+
ions from a solution of Cu
2+
2+
13
(aq.) is to add NH3(aq). A blue color signifies
2+
the formation of complex ⎡⎣Cu (NH3 )4 ⎤⎦ having Kf = 1.1 × 10 and thus confirms the presence of Cu in
solution.250mL of 0.1 MCuSO4(aq) is electrolyzed by passing a current of 3.512 ampere for 1368 second. After
passage of this charge sufficient quantity of NH3(aq.) is added to electrolyzed solution maintaining
[NH3 ]=0.10M. If
2+
⎡⎣Cu (NH3 )4 ⎤⎦ is detectable upto its concentration as low as 1× 10 −5 , would a blue colour be
shown by the electrolyzed solution on addition of NH3.
[Ans : Yes]
CHAPTER PRACTICE PROBLEMS
CHEMISTRY
FIITJEE
11. A current of 40 microampere is passed through a solution of AgNO3 for 32 minute using Pt electrodes. An
uniform single atom thick layer of Ag is deposited covering 43% cathode surface. What is the total surface
-16
2
area of cathode if each Ag atom covers.5.4 ×10 cm ?
2
[Ans : 601.65 cm ]
2+
12. A Zn rod weighing 25 g was kept in 100 ml of 1 MCuSO4 solution. After a certain time the molarity of Cu in
solution was 0.8. what was molarity of SO 24 − ? What was the mass of Zn rod after cleaning?(At.wt.Zn = 65.4)
[Ans : 23.6928g,no change in molarity]
13. Find the volume of gases evolved by passing 0.965 A current for 1 hr through an aqueous solution of
o
CH3COONa at 25 C and 1atm.
[Ans : 1.762L]
Electrochemical cells
14. In acidic medium MnO4− is an oxidizing agent.
MnO4− + 8H + + 5e − → Mn 2+
+
If H ion concentration is doubled, electrode potential of the cell MnO4− , Mn 2+ / Pt will
(A) increase by 28.46 mv
(B) decrease by 28.46 mv
(C) increase by 14.23 mv
(D) decreasing by 142.30 mv
[Ans: A]
15. Write both electrode reaction and overall cell reaction for the cell
Tl|TlCl(s) ||CdCl2(0.01 M)|Cd
0 +
0 2+
-3
and calculate EMF of the cell if E Tl / Tl = -0.34 V, E Cd /Cd = -0.40V &the solubility product of TlCl is 1.6 × 10 .
o
16. Find the e.m.f. of the following cell at 18 C taking the degree of dissociation of 0.2 M AgNO3 and 0.05 M
AgNO3 solution as 0.75 and 0.95 respectively Ag AgNO3 ( 0.2M,aq ) AgNO3 (0.05M,aq ) Ag .
[Ans :- 0.029V]
17. EMF diagram for same ions is given as :
o
o
o
E =+2.20V
E =+0.77V
E =−0.445V
FeO24− ⎯⎯⎯⎯⎯
→Fe3+ ⎯⎯⎯⎯⎯
→Fe2+ ⎯⎯⎯⎯⎯
→Fe
o
Determine the value of EFeO2− /Fe2+
4
[Ans : 1.84V]
18. The half cell potentials of a half cell A +( x +n) ,A x + Pt were found to be as follows:
% of reduced form
24.4
Half cell potential (V) 0.101
Determine the value of n.
48.8
0.115
[Ans :n =2]
19. An alloy weighing 1.05 g of Pb-Ag was dissolved in desired amount of HNO3 and the volume was made 350
mL. An Ag electrode was dipped in solution and Ecell of the cell Pt, H2 H+ Ag+ Ag was 0.503V at 298 K.
1 atm 1 M
calculate percentage of lead in alloy .(Given E
o
Ag+ / Ag
=0.80V).
[Ans : 99.967%]
2+
2+
20. Estimate the cell potential of a Daniel cell having 1.0 M Zn and originally having 1.0 M Cu after sufficient
ammonia has been added to the cathode compartment to make the NH3 concentration 2.0 M. Given
2+
EoZn/ Zn2+ and EoCu/CU2+ are 0.76 and -0.34V respectively. Also equilibrium constant for the ⎡⎣Cu (NH3 )⎤⎦ formation
is 1 × 10
12
[Ans :0.71V]
CHEMISTRY
CHAPTER PRACTICE PROBLEMS
FIITJEE
21. Match Column – I with Column – II
Column – I
(A)
Pt, Hg, Hg2Cl2, Cl
(B)
(C)
-
Column – II(Electrode or cell)
(P)
Daniell cell
Zn/ZnSO4(aq) //CuSO4(aq) /Cu
(Q)
Calomel electrode
Pt, H2(P1), HCl(1M) // HCl (1 M), H2(P2), Pt
(R)
SHE
(S)
Concentration cell
[Ans : A : Q, B : P, C : S, D : R]
(D)
Pt, H2 (1 atm), HCl (1M)
22. Match Column – I with Column – II
Column – I
Column – II
0.0591
=−
logQ
n
(A)
Arrhenius equation
(P)
Ecell0
(B)
Nernst equation for concentration cell
(Q)
K = Ae−Ea / RT
(C)
Nernst equation for Equilibrium
(R)
E0cell = E0cathode − E0anode
(D)
Electrode potential of the cell in standard conditions
(S)
Ecell = −
0.0591
logQ
n
[Ans : A : Q, B : S, C : P, D : R]
Electode potential
23. If EFe2t / Fe = x1, E o Fe3+ / Fe = x2 , then E o Fe3+ / Fe2+ is
(A) 3x2 − 2x1
(B) x2 − x1
(C) x2 + x1
(D) 2x1 − 3x2
[Ans : A]
Concentration Cells
-13
24. Ksp for AgBr = 8 × 10 . What is the e.m.f. of the cell:
Ag, AgNO3 (1.0M) || KBr (1.0 M), AgBr, Ag
25. Zn Zn 2 + ( c1 ) Zn 2 + (c2 ) Zn for this cell ΔG is negative if
(A) c1 = c2
(B) c1 > c2
(C) c2 > c1
(D) none of these
[Ans : C]
26. Pt , H2 ( P1 ) H + (1M ) H + (1M ) H 2 (P2 ) , where P1 & P2 are pressures. The cell reaction will be spontaneous if
(A) P1 = P2
(B) P1 > P2
(C) P2 > P1
(D) P1 = 1atm
[Ans : B]
27. For the given cell Ag AgCl (1M ) Ag 2SO4 (1M ) Ag Ecell is
(A) 0.0591V
(B) (0.0591× log2)V
(C) (0.0591× 2V )
(D) zero
[Ans : D]
28. A concentration cell has Zn electrodes. The electrolyte in each of the half-cells is a solution of ZnCl2 dissolved
0
0
in water. One has a freezing point of – 2.0 C and the other has a freezing point of -0.9 C. What is the
0
potential of the cell at 25 C?
Gibb’s Free Energy
29. The free energy of the formation of NO is 78 kJ/mole at the temperature 1000K of an automobile engine .
What is the equilibrium constant for this reaction at 1000k?
1
1
N2 (g ) + O2 (g )
2
2
NO(g)
-4
[Ans: 10 ]
CHAPTER PRACTICE PROBLEMS
FIITJEE
CHEMISTRY
(
)
30. Under which circumstance would the free energy change ΔG0 for a reaction
be relatively temperature independent?
(A) ΔH o is negative
(C) ΔS o has a large positive value
(B) ΔH o is positive
(D) ΔS o has a small positive
[Ans: D]
31. the free energy change for the following reaction is ΔG o = +63.3kj/mol .Calculate Ksp of Ag2CO3(s) in water at
o
25 C
+
Ag2CO3(S)
Ag (aq) + CO32 − (aq)
-11
[Ans: 10 ]
Multi concepts
32. Match Column – I with Column – II
Column – I
Column – II
(A)
ΔG
(B)
ΔG
(C)
Spontaneous process
(D)
At Equilibrium, ΔG
o
o
(P)
- RT lnKc
(Q)
- n FEcell(Ecell > 0)
(R)
- n FE
(S)
Ecell is positive
o
o
cell(E cell >
0)
[Ans : A : Q;B : P,R; C : Q,R,S; D:P ]