JEE Previous Year Questions (2021-23): Electrochemistry PDF Download

Q.1. The d-electronic configuration of [CoCl₄]²⁻ in tetrahedral crystal field is Sum of "m" and "number of unpaired electrons" is     (JEE Main 2023)

Ans. CO⁺³ → 3d⁷

Q.2. At 298 K, a 1 litre solution containing 10mmol of  and 100mmol of Cr³⁺ shows a pH of 3.0.
Given:  → Cr³⁺; E^∘ = 1.330 V and     (JEE Main 2023)

Ans. 917

Q.3. Consider the strong electrolytes Z_mX_n,U_mY_p and V_mX_n. Limiting molar conductivity ( Λ⁰ ) of U_mY_p and V_mX_n are 250 and 440 S cm² mol⁻¹, respectively. The value of (m+n+p) is
Given:     (JEE Advance 2022)

λ⁰ is the limiting molar conductivity of ions
The plot of molar conductivity Z_mX_nvsc^1/2 is given below.

Ans. 7

Q.4. The reduction potential    (JEE Advance 2022)
Given

Ans. 0.74 - 0.80

Q.5. For a cell, the cell potential is found to be 0.43 V at 298 K. The magnitude of standard electrode potential for Cu²⁺/Cu is _________ x 10^-2V.    (JEE Main 2022)

Ans. 34

Q.6.  Resistance of a conductivity cell (cell constant  129 m⁻¹) filled with 74.5ppm solution of KCl is 100Ω (labelled as solution 1). When the same cell is filled with KCl solution of 149ppm, the resistance is 50Ω (labelled as solution 2). The ratio of molar conductivity of solution 1 and solution 2 is i.e.  The value of x is __________. (Nearest integer)
Given, molar mass of KCl is 74.5 g mol^-1      (JEE Main 2022)

Ans. 1000

Q.7. The amount of charge in F (Faraday) required to obtain one mole of iron from Fe₃O₄ is ___________. (Nearest Integer)      (JEE Main 2022)

Ans. 8
for Fe₃O₄

x= +8/3
where x is oxidation state of Fe.

Q.8. The spin-only magnetic moment value of M³⁺ ion (in gaseous state) from the pairs Cr³⁺ / Cr²⁺, Mn³⁺ / Mn²⁺, Fe³⁺ / Fe²⁺ and Co³⁺ / Co²⁺ that has negative standard electrode potential, is ____________ B.M. [Nearest integer]       (JEE Main 2022)

Ans. 4
Among the pairs given, Cr³⁺ / Cr²⁺ has negative reduction potential which is -0.41 V

Number of unpaired electrons = 3

Q.9. The cell potential for Zn|Zn²⁺(aq)||Sn^x+|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 ____________.        (JEE Main 2022)
(Given:  )

Ans. 4

From the Nernst equation,

Q.10. The enthalpy of combustion of propane, graphite and dihydrogen at  298 K are −2220.0 kJ mol⁻¹,−393.5 kJ mol⁻¹ and   −285.8 kJ mol⁻¹ respectively. The magnitude of enthalpy of formation of propane (C₃H₈) is _______________ kJmol⁻¹. (Nearest integer)        (JEE Main 2022)

Ans. 104
Enthalpy of combustion of propane, graphite and H₂ at 298K  are

The desired reaction is

Q.11. The cell potential for the following cell Pt |H₂(g)|H⁺ (aq)|| Cu²⁺ (0.01 M)|Cu(s) is 0.576 V at 298 K. The pH of the solution is __________. (Nearest integer)        (JEE Main 2022)
Given: ()

Ans. 5

Q.12. The resistance of a conductivity cell containing 0.01 M KCl solution at 298 K is 1750 Ω. If the conductivity of 0.01 M KCl solution at 298 K is 0.152 x 10³ S cm^-1, then the cell constant of the conductivity cell is ____________  x 10^-3 cm^-1.        (JEE Main 2022)

Ans. 266
Molarity of KCl solution = 0.1 M
Resistance = 1750 ohm
Conductivity = 0.152x 10^-3 

Cell constant = 0.152x 10^-3 x 1750
= 266 x 10^-3_cm^-1

Q.13. In a cell, the following reactions take place    

The standard electrode potential for the spontaneous reaction in the cell is x  102 V 298 K. The value of x is ____________. (Nearest Integer)         (JEE Main 2022)

Ans. 23

Q.14. A solution of Fe₂(SO₄)₃ is electrolyzed for 'x' min with a current of 1.5 A to deposit 0.3482 g of Fe. The value of x is ___________. [nearest integer]         (JEE Main 2022)
Given : 1 F = 96500 C mol^-1, Atomic mass of Fe = 56 g mol^-1

Ans. 20

Q.15.
The Gibbs free energy change for the above reaction at 298 K is x  10^-1 kJ mol^-1. The value of x is __________. [nearest integer]         (JEE Main 2022)

Ans. 983

Q.16. The limiting molar conductivities of NaI, NaNO₃ and AgNO₃ are 12.7, 12.0 and 13.3 mS m² mol^-1, respectively (all at 25°C). The limiting molar conductivity of AgI at this temperature is ____________ mS m² mol^-1.          (JEE Main 2022)

Ans. 14

Q.17. For the reaction taking place in the cell :

The value of Δ_fG is ______________ kJ mol^-1. (in nearest integer)         (JEE Main 2022)

Ans. 103

# At anode, oxidation occur

# At cathode, reduction occur

Adding equation (1) and (2), we get n = 2, where n = cancelled out electron

Now,

Q.18. The quantity of electricity in Faraday needed to reduce 1 mol of    is ____________.           (JEE Main 2022)

Ans. 6

Q.19. For the given reactions

the electrode potentials are ;  The magnitude of standard electrode potential for  x 10^-2V.   (Nearest integer)           (JEE Main 2022)

Ans. 16

Q.20. 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 ___________.         (JEE Main 2022)

Ans. 7

Q.21. 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 a STP is _____________ cm3. (Nearest integer)           (JEE Main 2022)
[Given : Faraday constant F = 96500 C mol^-1 at STP, molar volume of an ideal gas is 22.7 L mol^-1]     

Ans. 127

Q.22. Match List - I with List - II.    (JEE Main 2022)
Choose the correct answer from the options given below:
(a) (A)−(I),(B)−(II),(C)−(III),(D)−(IV)  
(b) (A)−(IV),(B)−(I),(C)−(II),(D)−(III)  
(c) (A)−(II),(B)−(I),(C)−(IV),(D)−(III)  
(d) (A)−(II),(B)−(I),(C)−(III),(D)−(IV)

Ans. c

(a) Cd(s)+2Ni(OH)₃( s)→CdO(s)+2Ni(OH)₂( s) +H₂O(l) Discharge of secondary Battery
(b) Zn(Hg)+HgO (s) →ZnO(s)+Hg(l) (Primary Battery Mercury cell)

(c)  2PbSO₄( s)+2H₂O(l)→Pb(s)+PbO₂( s)+2H₂SO₄(aq) (Charging of secondary Battery)

(d)   2H₂( g)+O₂( g)→2H₂O(l) (Fuel cell)

Q.23. Given below are two statements :              (JEE Main 2022)
Statement I : For KI, molar conductivity increases steeply with dilution
Statement II : For carbonic acid, molar conductivity increases slowly with dilution
In the light of the above statements, choose the correct answer from the options given below:
(a) Both Statement I and Statement II are true  
(b) Both Statement I and Statement II are false  
(c) Statement I is true but Statement II is false  
(d) Statement I is false but Statement II is true

Ans. b
For any electrolyte, molar conductivity decreases with dilution.

Both Statements are false.

Q.24. The molar conductivity of a conductivity cell filled with 10 moles of 20 mL NaCl solution is Λ_m1 and that of 20 moles another identical cell heaving 80 mL NaCl solution is Λ_m2. The conductivities exhibited by these two cells are same. The relationship between Λ_m2 and Λ_m1 is               (JEE Main 2022)
(a)
(b)
(c)
(d)

Ans. a

It is given that k₁ = k₂

Applying the given condition on conductivity.

Q.25. In which of the following half cells, electrochemical reaction is pH dependent?               (JEE Main 2022)
(a) Pt|Fe³⁺,Fe²⁺ 
(b) MnO₄⁻|Mn²⁺ 
(c) Ag|AgCl|Cl⁻¹ 
(d) 1/2F₂|F⁻

Ans. b
Reduction of MnO₄⁻ is pH dependent.
In acidic medium

MnO₄⁻+5e⁻ ⟶ Mn²⁺

In neutral medium

MnO₄⁻+3e⁻ ⟶ Mn⁴⁺

In basic medium

MnO₄⁻+e ⟶ Mn⁶⁺

So, according to pH, the reaction and potential of cell changes.

Q.26. The correct order of reduction potentials of the following pairs is
A. Cl₂/Cl⁻
B. I₂/I⁻
C. Ag⁺/Ag
D. Na⁺/Na

E. Li⁺/Li
Choose the correct answer from the options given below.               (JEE Main 2022)
(a) A > C > B > D > E  
(b) A > B > C > D > E  
(c) A > C > B > E > D  
(d) A > B > C > E > D

Ans. a

Q.27. The  of different types of half cells are as follows:

(Where E is the electromotive force)

Which of the above half cells would be preferred to be used as reference electrode?               (JEE Main 2022)
(a) A
(b) B
(c) C
(d) D

Ans. c
A cell with less variation in EMF with temperature is preferred as a reference electrode because it can be used for a wider range of temperatures without much derivation from standard value so a cell with less   is preferred.

Q.28. In 3d series, the metal having the highest M²⁺/M standard electrode potential is                (JEE Main 2022)
(a) Cr
(b) Fe
(c) Cu
(d) Zn

Ans. c

Q.29. At 298 K, the limiting molar conductivity of a weak monobasic acid is 4 x 10² S cm² mol^-1. At 298 K, for an aqueous solution of the acid the degree of dissociation is α and the molar conductivity is y x 10² S cm² mol^-1. At 298 K, upon 20 times dilution with water, the molar conductivity of the solution becomes 3y x  10² S cm² mol^-1.

The value of y is __________.     (JEE Advance 2021)

Ans. 0.86
Degree of dissociation = α
Limiting molar conductivity,
Molar conductivity,

Molar conductivity of dilution,

Concentration before dilution = C

Concentration after dilution = c/20
Using relation,
Dissociation constant,
Putting Eq. (i),

Dissociation constant before dillution,

Dissociation constant after dilution,

Comparing Eqs. (ii) and (iii),

Q.30. At 298 K, the limiting molar conductivity of a weak monobasic acid is 4  102 S cm2 mol1. At 298 K, for an aqueous solution of the acid the degree of dissociation is  and the molar conductivity is y x 10² S cm² mol^-1. At 298 K, upon 20 times dilution with water, the molar conductivity of the solution becomes 3y  10² S cm² mol^-1.
The value of α is __________.    (JEE Advance 2021)

Ans. 0.22

Degree of dissociation = α
Limiting molar conductivity,
Molar conductivity,

Molar conductivity of dilution,

Concentration before dilution = C

Concentration after dilution = c/20
Using relation,
Dissociation constant,
Putting Eq. (i),

Dissociation constant before dillution,

Dissociation constant after dilution,

Comparing Eqs. (ii) and (iii),


Putting in Eq. (i),

The value of α  is 0.22.

Q.31. If the conductivity of mercury at 0°C is 1.07  10⁶ S m^-1 and the resistance of a cell containing mercury is 0.243Ω, then the cell constant of the cell is x * 10⁴ m^-1. The value of x is ____________. (Nearest integer)           (JEE Main 2021)

Ans. 26
Conductance (G) is reciprocal of resistance (R)
Relation between conductance (G),
conductivity (k) and cell constant(l/A)is given as

Q.32. Consider the following cell reaction :          (JEE Main 2021)

The value of  is 4.315 V at 25°C. If H = -825.2 kJ mol^-1, the standard entropy change ΔS° in J K^-1 is ___________. (Nearest integer) [Given : Faraday constant = 96487 C mol^-1]

Ans. 25



Nearest integer answer is 25.

Q.33. The resistance of a conductivity cell with cell constant 1.14 cm^-1, containing 0.001 M KCl at 298 K is 1500Ω . The molar conductivity of 0.001 M KCl solution at 298 K in S cm² mol^-1 is ____________. (Integer answer)          (JEE Main 2021)

Ans. 760

Q.34. For the galvanic cell,

E_cell = ______________  10^-2 V. (Nearest integer)          (JEE Main 2021)

Ans. 109
Galvanic cell:

Q.35. 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 the nearest integer).
[Use : 2.303RT/F = 0.059]          (JEE Main 2021)

Ans. 28
Cell reaction is:

Q.36. The conductivity of a weak acid HA of concentration 0.001 mol L^-1 is 2.0  10^-5 S cm^-1. If Λ°_m(HA) = 190 S cm² mol^-1, the ionization constant (K_a) of HA is equal to ______________  10^-6. (Round off to the Nearest Integer)           (JEE Main 2021)

Ans. 12

Q.37. Consider the cell at 25^∘C
Zn | Zn²⁺ (aq), (1M) || Fe³⁺ (aq), Fe²⁺ (aq) | Pt(s)
The fraction of total iron present as Fe³⁺ ion at the cell potential of 1.500 V is x * 10⁻². The value of x is ______________. (Nearest integer)           (JEE Main 2021)

Ans. 24

Q.38. Assume a cell with the following reaction

E_cell for the above reaction is ______________ V. (Nearest integer) 
[Given : log 2.5 = 0.3979, T = 298 K]             (JEE Main 2021)

Ans. 3

Q.39. Potassium chlorate is prepared by electrolysis of KCl in basic solution as shown by following equation.

A current of xA has to be passed for 10h to produce 10.0g of potassium chlorate. The value of x is ____________. (Nearest integer) (Molar mass of KClO₃ = 122.6 g mol^-1, F = 96500 C)             (JEE Main 2021)

Ans. 1

Q.40. The molar conductivities at infinite dilution of barium chloride, sulphuric acid and hydrochloric acid are 280, 860 and 426 S cm² mol^-1 respectively. The molar conductivity at infinite dilution of barium sulphate is _________ S cm² mol^-1. (Round off to the Nearest Integer ).              (JEE Main 2021)

Ans. 288
From Kohlrausch's law

Q.41. For the reaction the magnitude of the standard molar free energy change, ΔrG°_m =  ___________ kJ (Round off to the Nearest Integer).  (JEE Main 2021)
             

Ans. 46

Q.42. A KCl solution of conductivity 0.14 S m^-1 shows a resistance of 4.19Ω in a conductivity cell. If the same cell is filled with an HCl solution, the resistance drops to 1.03Ω. The conductivity of the HCl solution is ____________  10^-2 S m^-1. (Round off to the Nearest Integer).             (JEE Main 2021)

Ans. 57
For KCl solution,

For HCl solution,

Q.43. A 5.0 m mol dm^-3 aqueous solution of KCl has a conductance of 0.55 mS when measured in a cell of cell constant 1.3 cm^-1. The molar conductivity of this solution is ___________ mSm² mol^-1. (Round off to the Nearest Integer).            (JEE Main 2021)

Ans. 14

Q.44. Emf of the following cell at 298K in V is x *  10^-2. 
Zn|Zn²⁺(0.1 M)||Ag⁺ (0.01 M)|Ag
The value of x is _________. (Rounded off to the nearest integer)               (JEE Main 2021)

Ans. 147

Q.45. Consider the following reaction

The quantity of electricity required in Faraday to reduce five moles of MnO₄^- is ___________. (Integer answer)             (JEE Main 2021)

Ans. 25

1 mole of MnO4- required 5 moles of electrons or 5 F electricity.

∴ 5 moles of MnO₄^- required 25 F electricity.

Q.46. Among the following, number of metal/s which can be used as electrodes in the photoelectric cell is _________. (Integer answer)             (JEE Main 2021)
(a) Li
(b) Na
(c) Rb
(d) Cs

Ans. 1
Among the given alkali metals, only cesium (Cs) is used as electrode in the photoelectric cell due to its lowest ionisation energy.

Q.47. Electromagnetic radiation of wavelength 663 nm is just sufficient to ionise the atom of metal A. The ionization enegy of metal A in kJ mol1 is __________. (Rounded off to the nearest integer)  
[h = 6.63  10^-34 Js, c = 3.00 x 10⁸ ms^-1, N_A = 6.02 x 10²³ mol^-1]            (JEE Main 2021)

Ans. 180
Energy of EMR = IE of the metal (A)

Q.48. Copper reduces NO₃^- into NO and NO₂ depending upon the concentration of HNO₃ in solution. (Assuming fixed [Cu²⁺] and  the HNO₃ concentration at which the thermodynamic tendency for reduction of NO₃^- into NO and NO₂ by copper is same is 10^x M. The value of 2x is _______. (Rounded off to the nearest integer)           (JEE Main 2021)

Ans. 1

Q.49. 1 molal aqueous solution of an electrolyte A₂B₃ is 60% ionised. The boiling point of the solution at 1 atm is _________ K. (Rounded off to the nearest integer)

[Given Kb for (H₂O) = 0.52 K kg mol^-1]           (JEE Main 2021)

Ans. 375

Q.50. The magnitude of the change in oxidising power of the MnO₄⁻/Mn²⁺ couple is x * 10⁻⁴ V, if the H⁺ concentration is decreased from 1M to 10⁻⁴ M at 25°C. (Assume concentration of MnO₄⁻ and Mn²⁺ to be same on change in H+ concentration). The value of x is ___________.   [Given:2.303RT/F=0.059]           (JEE Main 2021)

Ans. 3776
Reaction,

Applying Nernst equation,

Q.51. Match List - I with List - II

Choose the most appropriate answer from the options given below:
(a) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)  
(b) (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)  
(c) (a)-(i), (b)-(iv), (c)-(iii), (d)-(ii)  
(d) (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)

Ans. a

Q.52. Given below are two statements:
Statement I: The limiting molar conductivity of KCl (strong electrolyte) is higher compared to that of CH₃COOH (weak electrolyte).
Statement II: Molar conductivity decreases with decrease in concentration of electrolyte.
In the light of the above statements, choose the most appropriate answer from the options given below:
(a) Statement I is true but Statement II is false.
(b) Statement I is false but Statement II is true.  
(c) Both Statement I and Statement II are true.  
(d) Both Statement I and Statement II are false.

Ans. d

So,

So, Statement I is wrong or false.
As the concentration decreases, the dilution increases which increases the degree of dissociation, thus increasing the no. of ions, which increases the molar conductance.
So Statement II is false.

Q.53. Given below are two statements :
Statement I: The Eo value for Ce⁴⁺ / Ce³⁺ is + 1.74 V.
Statement II: Ce is more stable in Ce⁴⁺ state than Ce³⁺ state.
In the light of the above statements, choose the most appropriate answer from the options given below:
(a) Statement I is incorrect but statement II is correct
(b) Both statement I and statement II are correct
(c) Both statement I and statement II are incorrect
(d) Statement I is correct but statement II is incorrect

Ans. d

Positive SRP and higher SRP means greater oxidising power. So, Ce⁴⁺ wants to reduce to Ce³⁺. Indicates Ce⁴⁺ is less stable than Ce³⁺.

Q.54. The electrode potential of M²⁺/M of 3d-series elements shows positive value for:
(a) Zn
(b) Fe
(c) Cu
(d) Co

Ans. c
In the electrode potential series, only copper have positive value for electrode potential because copper has lower tendency than hydrogen to form ions. So, if standard hydrogen electrode (E_Cell = 0) is connected to copper half-cell, the copper with be relatively less negative or less number of electrons.

∴ Electrode potential of Cu  show positive value.