CBSE Class 12 Chemistry Electrochemistry MCQs Set B

Question. The standard electrode potential (E°) values of Al³⁺/Al, Ag⁺/Ag, K⁺/K and Cr³⁺/Cr are –1.66 V, 0.80 V, –2.93 V and –0.74 V, respectively. The correct decreasing order of reducing power of the metal is
(a) Ag > Cr > Al > K
(b) K > Al > Cr > Ag
(c) K > Al > Ag > Cr
(d) Al > K > Ag > Cr

Answer : B

Question. A button cell used in watches function as following :
Zn_(s) + Ag₂O(s) + H₂O(l) ⇌ 2Ag(s) + Zn²⁺_(aq) + 2OH^–_(aq)
If half cell potentials are
Zn²⁺_(aq) + 2e^– → Zn(s); E° = – 0.76 V
Ag₂O_(s) + H₂O(l) + 2e^– → 2Ag_(s) + 2OH–(aq); E° = 0.34 V
The cell potential will be
(a) 0.84 V
(b) 1.34 V
(c) 1.10 V
(d) 0.42 V 

Answer : C

Question. Standard reduction potentials of the half reactions are given below :
F_2(g) + 2e^– → 2F–_(aq) ; E° = + 2.85 V
Cl_2(g) + 2e^– → 2Cl^–_(aq) ; E° = + 1.36 V
Br₂(l) + 2e– → 2Br^–_(aq) ; E° = + 1.06 V
I₂(s) + 2e– → 2I^–_(aq) ; E° = + 0.53 V
The strongest oxidising and reducing agents respectively are
(a) F₂ and I–
(b) Br₂ and Cl^–
(c) Cl₂ and Br–
(d) Cl₂ and I₂

Answer : A

Question. Standard electrode potentials of three metals X, Y and Z are –1.2 V, + 0.5 V and – 3.0 V respectively.
The reducing power of these metals will be
(a) Y > Z > X
(b) Y > X > Z
(c) Z > X > Y
(d) X > Y > Z

Answer : C

Question. Standard electrode potential for Sn⁴⁺/Sn²⁺ couple is +0.15 V and that for the Cr³⁺/Cr couple is –0.74 V. These two couples in their standard state are connected to make a cell. The cell potential will be
(a) + 1.19 V
(b) + 0.89 V
(c) + 0.18 V
(d) + 1.83 V

Answer : B

Question. A solution contains Fe²⁺, Fe³⁺ and I– ions. This solution was treated with iodine at 35°C. E° for Fe³⁺/Fe²⁺ is + 0.77 V and E° for I₂/2I– = 0.536 V. The favourable redox reaction is
(a) I₂ will be reduced to I–
(b) there will be no redox reaction
(c) I^– will be oxidised to I₂
(d) Fe²⁺ will be oxidised to Fe³⁺. 

Answer : C

Question. Consider the following relations for emf of an electrochemical cell
(i) EMF of cell = (Oxidation potential of anode) –(Reduction potential of cathode)
(ii) EMF of cell = (Oxidation potential of anode) + (Reduction potential of cathode)
(iii) EMF of cell = (Reductional potential of anode)+ (Reduction potential of cathode)
(iv) EMF of cell = (Oxidation potential of anode) – (Oxidation potential of cathode)
Which of the above relations are correct?
(a) (iii) and (i)
(b) (i) and (ii)
(c) (iii) and (iv)
(d) (ii) and (iv)

Answer : D

Question. On the basis of the following E° values, the strongest oxidizing agent is
[Fe(CN)₆]₄– → [Fe(CN)₆]₃– + e– ; E° = –0.35 V
Fe²⁺ → Fe³⁺ + e– ; E° = –0.77 V
(a) Fe³⁺
(b) [Fe(CN)₆]^3–
(c) [Fe(CN)₆]^4–
(d) Fe²⁺ 

Answer : A

Question. A hypothetical electrochemical cell is shown below : A/ A+ (x M)||B+(y M)|B
The emf measured is + 0.20 V. The cell reaction is
(a) A + B+ → A+ + B
(b) A+ + B → A + B+
(c) A+ + e– → A; B+ + e– → B
(d) the cell reaction cannot be predicted.

Answer : A

Question. E°Fe²⁺/Fe = – 0.441 V and E°Fe³⁺/Fe²⁺ = 0.771 V, the standard EMF of the reaction Fe + 2Fe³⁺ → 3Fe²⁺ will be
(a) 0.111 V
(b) 0.330 V
(c) 1.653 V
(d) 1.212 V

Answer : D

Question. The ion of least limiting molar conductivity among the following is
(a) SO₄^2-
(b) H⁺
(c) Ca²⁺
(d) CH₃COO^–

Answer : D

Question. Molar conductivities (∧⁰_m) at infinite dilution of NaCl, HCl and CH₃COONa are 126.4, 425.9 and 91.0 S cm² mol^–1 respectively. ∧⁰_m for CH₃COOH will be
(a) 425.5 S cm² mol^–1
(b) 180.5 S cm² mol^–1
(c) 290.8 S cm² mol^–1
(d) 390.5 S cm² mol^–1

Answer : D

Question. Which of the following statements regarding fuel cell is incorrect?
(a) These cells are eco-friendly.
(b) These cells convert energy of combustion of fuels like H₂, CH₄, CH₃OH etc., directly into electrical energy.
(c) H₂ – O₂ fuel cell is used in Apollo space programme.
(d) Fuel cells produce electricity with an efficiency of about 100%.

Answer : D

Question. The electric charge for electrode decomposition of one gram equivalent of a substance is
(a) one ampere per second
(b) 96500 coulombs per second
(c) one ampere for one hour
(d) charge on one mole of electrons

Answer : D

Question. In electrolysis of NaCl when Pt electrode is taken then H2 is liberated at cathode while with Hg cathode it forms sodium amalgam. This is because
(a) Hg is more inert than Pt
(b) more voltage is required to reduce H+ at Hg than at Pt
(c) Na is dissolved in Hg while it does not dissolve in Pt
(d) conc. of H+ ions is larger when Pt electrode is taken

Answer : B

Question. When 9650 coulombs of electricity is passed through a solution of copper sulphate, the amount of copper deposited is (given at. wt. of Cu = 63.6)
(a) 0318g
(b) 3.18 g
(c) 31.8g
(d) 63.6g

Answer : B

Question. A device that converts energy of combustion of fuels like hydrogen and methane, directly into electrical energy is known as :
(a) Electrolytic cell
(b) Dynamo
(c) Ni-Cd cell
(d) Fuel Cell

Answer : D

Question. A solution of copper sulphate (CuSO4) is electrolysed for 10 minutes with a current of 1.5 amperes. The mass of copper deposited at the cathode (at. mass of Cu = 63u) is
(a) 0.3892g
(b) 0.2938g
(c) 0.2398g
(d) 0.3928g

Answer : B

Question. When 0.1 mol MnO₄^2– is oxidised the quantity of electricity required to completely oxidise MnO₄^2– to MnO₄^– is
(a) 96500 C
(b) 2 × 96500 C
(c) 9650 C
(d) 96.50 C

Answer : C

Question.The weight of silver (at wt. = 108) displaced by a quantity of electricity which displaces 5600 mL of O₂ at STP will be
(a) 5.4 g
(b) 10.8 g
(c) 54.9 g
(d) 108.0 g

Answer : D

Question. Standard electrode potentials are Fe2+/Fe;
E° = –0.44 and Fe³⁺/Fe²⁺; E° = 0.77. Fe²⁺, Fe³⁺ and Fe blocks are kept together, then
(a) Fe³⁺ increases
(b) Fe3+ decreases
(c) Fe²⁺/Fe³⁺ remains unchanged
(d) Fe²⁺ decreases.

Answer : B

Question. Electrode potential for the following half-cell reactions are
Zn → Zn²⁺ + 2e–; E° = + 0.76 V;
Fe → Fe2+ + 2e–; E° = + 0.44 V.
The EMF for the cell reaction
Fe²⁺ + Zn → Zn²⁺ + Fe will be
(a) – 0.32 V
(b) + 1.20 V
(c) – 1.20 V
(d) + 0.32 V

Answer : D

Question. An electrochemical cell is set up as :
Pt; H₂ (1 atm)|HCl(0.1 M) || CH₃COOH (0.1 M) |H₂ (1 atm); Pt. The e.m.f. of this cell will not be zero, because
(a) acids used in two compartments are different
(b) e.m.f. depends on molarities of acids used
(c) the temperature is constant
(d) pH of 0.1 M HCl and 0.1 M CH₃COOH is not same. 

Answer : D

Question. Standard reduction potentials at 25°C of Li+|Li, Ba²⁺|Ba, Na⁺|Na and Mg²⁺|Mg are –3.05, –2.90,–2.71 and –2.37 volt respectively. Which one of the following is the strongest oxidising agent?
(a) Ba²⁺
(b) Mg²⁺
(c) Na⁺
(d) Li⁺ 

Answer : B

Question. A solution of potassium bromide is treated with each of the following. Which one would liberate bromine?
(a) Hydrogen iodide
(b) Sulphur dioxide
(c) Chlorine
(d) Iodine

Answer : C

Question. For the cell reaction :
2Fe³⁺_(aq) + 2I–(aq) 2Fe²⁺_(aq) + I_2(aq)
E°_cell = 0.24 V at 298 K. The standard Gibbs’ energy (ΔrG°)of the cell reaction is
[Given that Faraday constant, F = 96500 C mol^–1]
(a) 23.16 kJ mol^–1
(b) –46.32 kJ mol^–1
(c) –23.16 kJ mol^–1
(d) 46.32 kJ mol^–1

Answer : B

Question. In the electrochemical cell : Zn|ZnSO₄₍0.01 M)||CuSO₄(1.0 M)|Cu, the emf of this Daniell cell is E1. When the concentration of ZnSO₄ is changed to 1.0 M and that of CuSO4 changed to 0.01 M, the emf changes to E₂. From the followings, which one is the relationship between E₁ and E₂? (Given, RT/F = 0.059)
(a) E₁ < E₂
(b) E₁ > E₂
(c) E₂ = 0 ≠ E₁
(d) E₁ = E₂

Answer : B

Question. If the E°cell for a given reaction has a negative value,which of the following gives the correct relationships for the values of ΔG° and Keq ?
(a) ΔG° > 0; K_eq < 1
(b) ΔG° > 0; K_eq > 1
(c) ΔG° < 0; K_eq > 1
(d) ΔG° < 0; K_eq < 1

Answer : A

Question. The pressure of H₂ required to make the potential of H₂ electrode zero in pure water at 298 K is
(a) 10^–10 atm
(b) 10^–4 atm
(c) 10^–14 atm
(d) 10^–12 atm.

Answer : C

Question. A hydrogen gas electrode is made by dipping platinum wire in a solution of HCl of pH = 10 and by passing hydrogen gas around the platinum wire at one atm pressure. The oxidation potential of electrode would be
(a) 0.118 V
(b) 1.18 V
(c) 0.059 V
(d) 0.59 V

Answer : D

Question. Consider the half-cell reduction reaction
Mn²⁺ + 2e– → Mn, E° = – 1.18 V
Mn²⁺ → Mn³⁺ + e–, E° = – 1.51 V
The E° for the reaction, 3Mn²⁺ → Mn0 + 2Mn³⁺, and possibility of the forward reaction are respectively
(a) – 4.18 V and yes
(b) + 0.33 V and yes
(c) + 2.69 V and no
(d) – 2.69 V and no.

Answer : D

Question. For the reduction of silver ions with copper metal, the standard cell potential was found to be + 0.46 V at 25 °C. The value of standard Gibbs energy, DG° will be (F = 96500 C mol^–1)
(a) – 89.0 kJ
(b) – 89.0 J
(c) – 44.5 kJ
(d) – 98.0 kJ

Answer : A

Question. Given :
(i) Cu²⁺ + 2e– → Cu, E° = 0.337 V
(ii) Cu²⁺ + e– → Cu+, E° = 0.153 V
Electrode potential, E° for the reaction,
Cu⁺ + e– → Cu, will be
(a) 0.90 V
(b) 0.30 V
(c) 0.38 V
(d) 0.52 V

Answer : D

Question. Standard free energies of formation (in kJ/mol) at 298 K are –237.2, –394.4 and –8.2 for H₂O(l), CO₂(g) and pentane(g) respectively. The value of E°cell for the pentane-oxygen fuel cell is
(a) 1.0968 V
(b) 0.0968 V
(c) 1.968 V
(d) 2.0968 V

Answer : A

Question. The equilibrium constant of the reaction :
Cu(s) + 2Ag⁺_(aq) → Cu²⁺(aq) + 2Ag(s);
E° = 0.46 V at 298 K is
(a) 2.0 × 10¹⁰
(b) 4.0 × 10¹⁰
(c) 4.0 × 10¹⁵
(d) 2.4 × 10¹⁰ 

Answer : C

Question. The standard e.m.f. of a galvanic cell involving cell reaction with n = 2 is found to be 0.295 V at 25°C.
The equilibrium constant of the reaction would be (Given F = 96500 C mol–1, R = 8.314 J K^–1 mol^–1)
(a) 2.0 × 10¹¹
(b) 4.0 × 10¹²
(c) 1.0 × 10²
(d) 1.0 × 10¹⁰

Answer : D

Question. On the basis of the information available from the reaction, 4/3Al + O₂ → 2/3Al₂O₃, ΔG = –827 kJ mol^–1 of O₂, the minimum e.m.f. required to carry out an electrolysis of Al2O3 is (F = 96500 C mol^–1)
(a) 2.14 V
(b) 4.28 V
(c) 6.42 V
(d) 8.56 V

Answer : A

Question. For the disproportionation of copper 2Cu⁺ → Cu²⁺ + Cu, E° is (Given : E° for Cu²⁺/Cu is 0.34 V and E° for Cu²⁺/Cu+ is 0.15 V)
(a) 0.49 V
(b) –0.19 V
(c) 0.38 V
(d) –0.38 V

Answer : C

Question. E° for the cell, Zn | Zn²⁺_(aq) ||Cu²⁺_(aq) | Cu is 1.10 V at 25°C, the equilibrium constant for the reaction Zn + Cu²⁺ _(aq) → Cu + Zn2+ (aq) is of the order
(a) 10⁺¹⁸ 
(b) 10⁺¹⁷
(c) 10^–28 
(d) 10⁺³⁷

Answer : D

Question. The molar conductivity of a 0.5 mol/dm³ solution of AgNO₃ with electrolytic conductivity of 5.76 × 10^–3 S cm^–1 at 298 K is
(a) 2.88 S cm²/mol
(b) 11.52 S cm²/mol
(c) 0.086 S cm²/mol
(d) 28.8 S cm²/mol

Answer : B

Question. For the following cell with hydrogen electrodes at two different pressures p₁ and p₂
Pt(H₂ ) l H⁺ (aq) l Pt (H₂ ) emf is given by Pt 1M P₂ 
(a) RT/F log_e P₁/P₂
(b) RT/2F log_e P₁/P₂
(c) RT/F log_e P₂/P₁
(d) RT/2F log_e P₂/P₁

Answer : B

Question. For a cell given below,
Ag l Ag⁺ ll Cu²⁺ l Cu
Ag⁺ +e^– → Ag,E° = x
Cu ²⁺ + 2e^– → Cu, E° = y E°_cell is
(a) x + 2y
(b) 2x + y
(c) y – x
(d) y – 2x

Answer : C

Question. A standard hydrogen electrode has zero electrode potential because
(a) hydrogen is easier to oxidise
(b) this electrode potential is assumed to be zero
(c) hydrogen atom has only one electron
(d) hydrogen is the lightest element

Answer : B

Question. For hydrogen-oxygen fuel cell at 1 atm and 298 K
H₂ (g) + 1/2 O₂ (g) → H₂O(l), ΔG = – 240 kJ
E° for the cell is approximately (Given, F = 96500 C)
(a) 2.48 V
(b) 1.25 V 
(c) 2.5 V
(d) 1.24 V 

Answer : D

Question. The rusting of iron takes place as follows
2H⁺ + 2e^– + 1/2 O₂ →H₂O(/);E° = + 1.23 V
Fe²⁺ + 2e^– → Fe (s);E° = – 0.44 V
Calculate ΔG° for the net process. 
(a) – 322 kJ mol^-1
(b) – 161 kJ mol^-1
(c) – 152 kJ mol^-1
(d) – 76 kJ mol^-1

Answer : A