Electrochemistry · Chemistry · COMEDK

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MCQ (Single Correct Answer)

1
For the cell reaction $4 \mathrm{Br}^{-}+\mathrm{O}_2+4 \mathrm{H}^{+} \rightarrow 2 \mathrm{Br}_2+2 \mathrm{H}_2 \mathrm{O}$ at 298 K , the $\mathrm{E}^0$ cell $=0.16 \mathrm{~V}$. What would be the $\mathrm{K}_{\mathrm{c}}$ (Equilibrium constant) value if the reverse reaction were to take place?
COMEDK 2025 Evening Shift
2

Two statements, one Assertion and the other Reason, are given. Choose the correct option.

Assertion : During the electrolysis of aqueous $\mathrm{NaCl}, \mathrm{Cl}_2$ is liberated at the anode in preference to $\mathrm{O}_2$ and water gets reduced to $\mathrm{H}_2$ at cathode.

Reason : The reaction at Anode with lower oxidation potential is not preferred due to over potential of Oxygen.

COMEDK 2025 Evening Shift
3
For a cell $2 \mathrm{M}_{(\mathrm{S})}+\mathrm{O}_2(\mathrm{~g})+4 \mathrm{H}^{+} \rightarrow 2 \mathrm{M}^{2+}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}$ the $\mathrm{E}^0$ cell $=+1.67 \mathrm{~V}$. When $\left[\mathrm{M}^{2+}\right]$ is $1.0 \times 10^{-3} \mathrm{M}$ and $\mathrm{p}\left(\mathrm{O}_2\right)$ is 0.1 atm , the EMF of the cell becomes +1.57 V . Calculate the pH of the electrochemical cell.
COMEDK 2025 Evening Shift
4

When $0.1 \mathrm{~mol} \mathrm{~L}^{-1}$ of KCl was filled in a Conductivity cell the resistance was 80 ohms at 298 K . (Conductivity of 0.1 M KCl at 298 K is $1.29 \mathrm{~S} \mathrm{~m}^{-1}$. The same cell when filled with an unknown electrolyte of concentration 0.025 M , had a resistance of 92 ohms. What is the Molar conductivity of the electrolyte at the given concentration?

COMEDK 2025 Evening Shift
5

Identify the two incorrect electrochemical reactions shown as taking place in the given cells at the respective electrodes.

Cell Electrode Reaction
Lead-Storage Cell Cathode $\mathrm{Pb}+2 \mathrm{SO}_4{ }^{2-}+4 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{PbSO}_4+2 \mathrm{H}_2 \mathrm{O}+\mathrm{SO}_2$
Leclanche Cell Cathode $\mathrm{MnO}_2+\mathrm{NH}_4^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{MnO}+\mathrm{OH}+\mathrm{NH}_3$
Mercury Cell Anode $\mathrm{Zn} / \mathrm{Hg}+2 \mathrm{OH}^{-} \rightarrow \mathrm{ZnO}(\mathrm{s})+\mathrm{H}_2 \mathrm{O}+2 \mathrm{e}^{-}$
Fuel Cell Cathode $\mathrm{O}_2(\mathrm{~g})+2 \mathrm{H}_2 \mathrm{O}+4 \mathrm{e}^{-} \rightarrow 4 \mathrm{OH}^{-}$

COMEDK 2025 Evening Shift
6

The $E_{M^{3+} / M^{2+}}^o$ values for $\mathrm{Cr}, \mathrm{Mn}, \mathrm{Fe}$ and Co are $-0.41,+1.57,+0.77$ and +1.97 V respectively.

For which of these metals, the change in oxidation state from +2 to +3 is the easiest?

COMEDK 2025 Afternoon Shift
7
What would be the cell potential for the Galvanic cell which is represented by the electrochemical reaction: $$ \begin{aligned} & 2 \mathrm{Cr}_{(\mathrm{S})}+3 \mathrm{Fe}^{2+}(0.02 \mathrm{M}) \rightarrow 2 \mathrm{Cr}^{3+}(0.2 \mathrm{M})+3 \mathrm{Fe} \\ & \mathrm{E}^0 \mathrm{Fe}^{2+} / \mathrm{Fe}=-0.42 \mathrm{~V} \quad \mathrm{E}^0 \mathrm{Cr}^{3+} / \mathrm{Cr}=-0.72 \mathrm{~V} \end{aligned} $$
COMEDK 2025 Afternoon Shift
8
A current of 1.5 A is passed for 2 hours through an aqueous solution of $\mathrm{PdX} \mathrm{n}_{\mathrm{n}}$ where X is a monovalent anion. During the electrolysis process 2.977 g of Palladium metal gets deposited at the cathode. Calculate the charge on Pd ions. (Atomic mass of $\mathrm{Pd}=106.4 \mathrm{~g} / \mathrm{mol}$ ).
COMEDK 2025 Afternoon Shift
9

What is the standard electrode potential at 298 K for the reaction: $\mathrm{Cu}^{2+}+1 \mathrm{e}-\rightarrow \mathrm{Cu}^{+1}$ ?

Given: $\mathrm{E}_0 \mathrm{Cu}^{+1} / \mathrm{Cu}=0.5 \mathrm{~V} \quad \& \quad \mathrm{E}_0 \mathrm{Cu}^{+2} / \mathrm{Cu}=0.335 \mathrm{~V}$

COMEDK 2025 Afternoon Shift
10

The Standard Reduction potential at $25^{\circ} \mathrm{C}$ for $\left(\mathrm{MnO}_4\right)^{-1} / \mathrm{H}^{+}$is +1.49 V . The $\mathrm{E}^0$ values for four Metal ions :

(a). $\mathrm{Co}^{3+} / \mathrm{Co}^{2+}$

(b). $\mathrm{Cr}^{3+} / \mathrm{Cr}$

(c). $\mathrm{Au}^{3+} / \mathrm{Au}$ and

(d). $\mathrm{Ag}^{+} / \mathrm{Ag}$

are $+1.81 \mathrm{~V},-0.74 \mathrm{~V},+1.50 \mathrm{~V}$ and +0.8 V respectively. Identify two of them which cannot be oxidised by $\left(\mathrm{MnO}_4\right)^{-1} / \mathrm{H}^{+}$

COMEDK 2025 Afternoon Shift
11

Two statements, one Assertion and the other Reason are given. Choose the correct option.

Assertion: For strong electrolytes the plot of Molar conductivity versus Concentration gives a straight line with slope equal to +A and intercept equal to $\lambda_{\mathrm{m}}$

Reason: For strong electrolytes, $\lambda_{\mathrm{m}}$ increases slowly with dilution due to increase in the distance between the ions and increase in ionic mobility

COMEDK 2025 Afternoon Shift
12
What is the reduction potential of a half-cell consisting of a Pt electrode dipped in $2.2 \mathrm{M} \mathrm{Fe}^{2+}$ and $0.04 \mathrm{M} \mathrm{Fe}^{3+}$ solution where the reaction taking place is conversion of $\mathrm{Fe}^{3+}$ ions to $\mathrm{Fe}^{2+}$ ?

$$\mathrm{E}^0\left(\mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}\right)=0.771 \mathrm{~V}$$

COMEDK 2025 Morning Shift
13
A current of 2.5 amperes is passed through 800 ml of 0.48 M solution of $\mathrm{CuSO}_4$ for 1.0 hour with a current efficiency of $80 \%$. If the volume of the solution remains unchanged, what is the final molarity of the solution?
COMEDK 2025 Morning Shift
14
The EMF of the cell $\mathrm{Al} / \mathrm{Al}^{3+}(0.01 \mathrm{M}) \| \mathrm{Fe}^{2+}(0.02 \mathrm{M}) / \mathrm{Fe}$ is 1.209 V . The EMF of the cell can be increased by
COMEDK 2025 Morning Shift
15

Identify the correct statement regarding corrosion of iron rod left exposed to atmosphere.

COMEDK 2024 Evening Shift
16

Given below are 2 statements: Assertion and Reason. Choose the correct option.

Assertion: When Molar conductivity for a strong electrolyte is plotted versus $$\sqrt{C}(\mathrm{~mol} / \mathrm{L})^{1 / 2}$$, a straight line is obtained with intercept equal to Molar conductivity at infinite dilution for the electrolyte and Slope equal to $$-\mathrm{A}$$. All electrolytes of a given type have the same $$\mathrm{A}$$ value.

Reason: At infinite dilution, strong electrolytes of the same type will have different number of ions due to incomplete dissociation.

COMEDK 2024 Evening Shift
17

What is the quantity of charge, in Faraday units, required for the reduction of 3.5 moles of $$\mathrm{Cr}_2 \mathrm{O} 7^{2-}$$ in acid medium?

COMEDK 2024 Evening Shift
18

A dry cell consists of a moist paste of $$\mathrm{NH}_4 \mathrm{Cl}$$ and $$\mathrm{ZnCl}_2$$ contained in a $$\mathrm{Zn}$$ casing which encloses a Carbon rod surrounded by black $$\mathrm{MnO}_2$$ paste. What is the role of $$\mathrm{ZnCl}_2$$ in it?

COMEDK 2024 Evening Shift
19

A current of 3.0A is passed through 750 ml of 0.45 M solution of CuSO$$_4$$ for 2 hours with a current efficiency of 90%. If the volume of the solution is assumed to remain constant, what would be the final molarity of CuSO$$_4$$ solution?

COMEDK 2024 Evening Shift
20

Arrange the following redox couples in the increasing order of their reducing strength:

$$\begin{array}{ll} {[\mathrm{A}]=\mathrm{Cu} / \mathrm{Cu}^{2+}} & \mathrm{E}^0=-0.34 \mathrm{~V} \\ {[\mathrm{~B}]=\mathrm{Ag} / \mathrm{Ag}^{+}} & \mathrm{E}^0=-0.8 \mathrm{~V} \\ {[\mathrm{C}]=\mathrm{Ca} / \mathrm{Ca}^{2+}} & \mathrm{E}^0=+2.87 \mathrm{~V} \\ {[\mathrm{D}]=\mathrm{Cr} / \mathrm{Cr}^{3+}} & \mathrm{E}^0=+0.74 \mathrm{~V} \end{array}$$

COMEDK 2024 Evening Shift
21

When 0.1 mole of $$\mathrm{MnO}_4{ }^{2-}$$ is oxidised, the quantity of electricity required to completely oxidise $$\mathrm{MnO}_4{ }^{2-}$$ to $$\mathrm{MnO}_4^{-}$$ is

COMEDK 2024 Afternoon Shift
22

Identify the incorrect statement among the following.

COMEDK 2024 Afternoon Shift
23

$$\mathrm{Cu}^{+}$$ undergoes disproportionation, according to the equation,

$$ 2 \mathrm{Cu}^{+} \rightleftharpoons \mathrm{Cu}^{2+}+\mathrm{Cu} $$

The $$\mathrm{E}^{\circ}$$ value for the reaction is:

$$[\mathrm{E}_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{\mathrm{o}}=0.34 \mathrm{~V} \text { and } \mathrm{E}_{\mathrm{Cu}^{2+} / \mathrm{Cu}^{+}}^{\mathrm{O}}=0.15 \mathrm{~V}]$$

COMEDK 2024 Afternoon Shift
24

The $$\mathrm{E}^{\circ}$$ values of $$\mathrm{A} . \mathrm{B}$$ and $$\mathrm{C}$$ are given. Which element/(s) is/(are) good for coating the surface of iron to prevent corrosion? Given: $$[\mathrm{E}_{\mathrm{Fe}^{2+} / \mathrm{Fe}}^0=-0.44 \mathrm{~V} ; \quad \mathrm{E}_{\mathrm{A}^{2+} / \mathrm{A}}^0=-2.37 \mathrm{~V} ; \quad \mathrm{E}_{\mathrm{B}^{2+} / \mathrm{B}}^0=-0.15 \mathrm{~V} ; \quad \mathrm{E}_{\mathrm{C}^{2+} / \mathrm{C}}^0=+0.34 \mathrm{~V}]$$

COMEDK 2024 Afternoon Shift
25

The limiting molar conductivity of $$\mathrm{NH}_4 \mathrm{OH}$$ is $$238 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$$. At $$25^{\circ} \mathrm{C}$$, molar conductance of $$0.1 \mathrm{M}$$ aqueous solution of ammonium hydroxide is $$9.54 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$$. The degree of ionisation of $$\mathrm{NH}_4 \mathrm{OH}$$ at the same concentration and temperature is:

COMEDK 2024 Afternoon Shift
26

What would be the EMF of the cell in which the following reaction occurs:

$$\begin{aligned} & \mathrm{Cd}(\mathrm{S})+2 \mathrm{H}^{+} \rightarrow \mathrm{Cd}^{2+}+\mathrm{H}_{2(\mathrm{~g})} \\ & {\left[\mathrm{H}^{+}\right]=0.02 \mathrm{M} \quad \mathrm{E}^0\left(\mathrm{Cd}^{2+} / \mathrm{Cd}\right)=-0.4 \mathrm{~V},\left[\mathrm{Cd}^{2+}\right]=0.01 \mathrm{M} \text { and partial pressure of } \mathrm{H}_2 \text { gas }=0.8 \mathrm{~atm} .} \end{aligned}$$

COMEDK 2024 Morning Shift
27

Propane in presence of $$\mathrm{O}_2$$ gas undergoes complete combustion to produce $$\mathrm{CO}_2$$ and $$\mathrm{H}_2 \mathrm{O}$$. The required $$\mathrm{O}_2$$ for this combustion reaction was produced by the electrolysis of water. For what duration of time had water been electrolysed by passing $$200 \mathrm{~A}$$ current so that Oxygen gas produced could completely burn $$44 \mathrm{~g}$$ of Propane?

COMEDK 2024 Morning Shift
28

$$0.1 \mathrm{M}$$ solution of $$\mathrm{AgNO}_3$$ is taken in a Conductivity cell and a potential difference of $$40 \mathrm{~V}$$ is applied across the ends of a column of this solution whose diameter is $$4.0 \mathrm{~cm}$$ and length of the column is $$12 \mathrm{~cm}$$. The current used is $$0.4 \mathrm{~A}$$. The Molar conductivity of the solution is _________.

COMEDK 2024 Morning Shift
29

Match the chemical reactions taking place at the Anode of the cell with the correct cell in which the reaction occurs.

No. Anodic reaction No. Cell
A $$
\mathrm{Zn}(\mathrm{Hg})+2 \mathrm{OH}^{-} \rightarrow \mathrm{ZnO}_{(\mathrm{S})}+\mathrm{H}_2 \mathrm{O}+2 e
$$
P Fuel cell
B $$
2 \mathrm{H}_2(g)+4 \mathrm{OH}^{-} \rightarrow 4 \mathrm{H}_2 \mathrm{O}(l)+4 e
$$
Q Leclanche cell
C $$
Z n_{(S)} \rightarrow Z n^{2+}+2 e
$$
R Nickel Cadmium storage cell
D $$
\mathrm{Cd}_{(S)}+2 \mathrm{OH}^{-} \rightarrow \mathrm{CdO}_{(S)}+\mathrm{H}_2 \mathrm{O}(l)+2 e
$$
S Mercury cell

COMEDK 2024 Morning Shift
30

Given below are 4 equations showing Molar conductivities at infinite dilution of various electrolytes. Which one of them represents the correct equation?

$$\begin{aligned} & \left(\Lambda_m^0\right)_{N a B r}-\left(\Lambda_m^0\right)_{N a C l}=\left(\Lambda_m^0\right)_{\mathrm{KCl}}-\left(\Lambda_m^0\right)_{\mathrm{KBr}} \\ & \left(\Lambda_m^0\right)_{\mathrm{HCl}}+\left(\Lambda_m^0\right)_{\mathrm{KOH}}-\left(\Lambda_m^0\right)_{\mathrm{KCl}}=\left(\Lambda_m^0\right)_{\mathrm{H}_2 \mathrm{O}} \\ & \left(\Lambda_m^0\right)_{\mathrm{KBr}}-\left(\Lambda_m^0\right)_{\mathrm{NaBr}}=\left(\Lambda_m^0\right)_{\mathrm{NaBr}}-\left(\Lambda_m^0\right)_{\mathrm{Nal}} \\ & \left(\Lambda_m^0\right)_{N H_4 \mathrm{Cl}}-\left(\Lambda_m^0\right)_{\mathrm{NH}_4 \mathrm{NO}_3}=\left(\Lambda_m^0\right)_{N H_4 \mathrm{Cl}}-\left(\Lambda_m^0\right)_{N H 4 B r} \end{aligned}$$

COMEDK 2024 Morning Shift
31

Assuming no change in volume, the time required to obtain solution of $$\mathrm{pH}=4$$ by electrolysis of $$100 \mathrm{~mL}$$ of $$0.1 \mathrm{~M} \mathrm{~NaOH}$$ (using current $$0.5 \mathrm{~A}$$ ) will be

COMEDK 2023 Morning Shift
32

For a cell reaction, $$A(s)+B^{2+}(a q) \longrightarrow A^{2+}(a q)+B(s)$$; the standard emf of the cell is $$0.295 \mathrm{~V}$$ at $$25^{\circ} \mathrm{C}$$. The equilibrium constant at $$25^{\circ} \mathrm{C}$$ will be

COMEDK 2023 Morning Shift
33

The Molar conductivity of $$0.05 \mathrm{M}$$ solution of $$\mathrm{MgCl}_2$$ is $$194.5 \mathrm{~ohm}^{-1} \mathrm{~cm}^2$$ per mole at room temperature. A Conductivity cell with electrodes having $$3.0 \mathrm{~cm}^2$$ surface area and $$1.0 \mathrm{~cm}$$ apart is filled with the solution of $$\mathrm{MgCl}_2$$. What would be the resistance offered by the conductivity cell?

COMEDK 2023 Evening Shift
34

If electrolysis of water is carried out for a time duration of 2 hours, how much electric current in amperes would be required to liberate $$100 \mathrm{~ml}$$ of $$\mathrm{O}_2$$ gas measured under standard conditions of temperature and pressure?

COMEDK 2023 Evening Shift
35

Match the items in Column I with their description in Column II

S.No. Column I S.No. Column II
A Kappa K P Intensive property.
B $$\mathrm{E_{cell}^0}$$ Q Extensive property.
C Molar conductivity R Decreases with decrease in concentration of both strong and weak electrolytes.
D $$\mathrm{\Delta G_{cell}}$$ S Increases with dilution.

COMEDK 2023 Evening Shift
36

When Lead Storage battery is in the process of getting charged which one of the following reactions takes place?

COMEDK 2023 Evening Shift
37

The reaction taking place in a galvanic cell is as given

$$\mathrm{A}(\mathrm{s})+\mathrm{B}^{2+}\left(\mathbf{1} \mathbf{1} \mathbf{1 0} \mathbf{0}^{-\mathrm{M}} \mathbf{M}\right) \rightarrow \mathrm{B}_{(\mathrm{s})}+\mathrm{A}^{2+}(0.1 \mathrm{M}).$$

The emf of the cell is $$+2.651 \mathrm{~V}$$. If the standard emf of the cell is $$+2.71 \mathrm{~V}$$, what is the value of $$\mathrm{X}$$ ?

COMEDK 2023 Evening Shift
38

What will be the emf of the following cell at 25$$^\circ$$C?

Fe/Fe$$^{2+}$$ (0.001 M) | | H$$^+$$ (0.01 M) | H$$_2$$(g) (1 Bar) | Pt(s)

$$E_{(F{e^{2+}} /Fe)}^o = - 0.44$$ V; $$E_{({H^ + }/{H_2})}^o = - 0.00$$ V

COMEDK 2022
39

Calculate the molar conductance of 0.025 M aqueous solution of calcium chloride at 25$$^\circ$$C. The specific conductance of calcium chloride is 12.04 $$\times$$ 10$$^{-2}$$ Sm$$^{-1}$$

COMEDK 2022
40

Given that molar conductances for Ba(OH)$$_2$$, BaCl$$_2$$ and NH$$_4$$Cl are 523.28, 280.0 and 129.8 $$\Omega^{-1}$$ cm$$^2$$ mol$$^{-1}$$ respectively. What is the molar conductivity ($$\Omega^{-1}$$ cm$$^2$$ mol$$^{-1}$$) of NH$$_4$$OH?

COMEDK 2021
41

The specific conductivity of a solution containing 1.0 g of anhydrous BaCl$$_2$$ in 200 cm$$^3$$ of the solution has been found to be 0.0058 Scm$$^{-1}$$. The molar and equivalent conductivity of the solution respectively are

COMEDK 2021
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