Electrochemistry · JEE Main previous year questions

In the Hall-Heroult process, aluminium is formed at the cathode. The cathode is made out of -

1. A.Copper
2. B.Platinum
3. C.Carbon
4. D.Pure aluminium

${\Lambda }_m^{\circ }$ for NaCl, HCl and NaA are 126.4, 425.9 and $100.5\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$, respectively. If the conductivity of 0.001 M HA is- $5\times 10^{-5}\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$, degree of dissociation of HA is -

1. A.0.50
2. B.0.125
3. C.0.25
4. D.0.75

The anodic half-cell of lead-acid battery is recharged using electricity of $0.05\text{ Faraday}$. The amount of $\mathrm{PbS}{\mathrm{O}}_4$ electrolyzed in g during the process is : (Molar mass of $\mathrm{PbS}{\mathrm{O}}_4=303{\text{ g mol}}^{-1}$)

1. A.22.8
2. B.15.2
3. C.7.6
4. D.11.4

When an electric currents passed through acidified water, 112 mL of hydrogen gas at N.T.P. was collected at the cathode in 965 seconds. The current passed, in ampere, is :

1. A.1.0
2. B.0.5
3. C.0.1
4. D.2.0

What is the standard reduction potential (${\mathrm{E}}^{\mathrm{o}}$) for $\mathrm{F}{\mathrm{e}}^{3+}\to \mathrm{Fe}$ ? Given that : $\mathrm{F}{\mathrm{e}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Fe};E_{\mathrm{F}{\mathrm{e}}^{2+}/Fe}^o=-0.47\mathrm{V}$ $\mathrm{F}{\mathrm{e}}^{3+}+{\mathrm{e}}^{-}\to \mathrm{F}{\mathrm{e}}^{2+};E_{\mathrm{F}{\mathrm{e}}^{3+}/F{\mathrm{e}}^{2+}}^o=+0.77\mathrm{V}$

1. A.$-0.057\mathrm{V}$
2. B.$+0.057\mathrm{V}$
3. C.$+0.30\mathrm{V}$
4. D.$-0.30\mathrm{V}$

Consider the following standard electrode potentials (${\mathrm{E}}^{\mathrm{o}}$ in volts) in aqueous solution : | Element | ${\mathrm{M}}^{3+}/M$ | ${\mathrm{M}}^{+}/M$ | |---|---|---| | Al | -1.66 | + 0.55 | | Tl | +1.26 | - 0.34 | Based on these data, which of the following statements is correct ?

1. A.$\mathrm{T}{\mathrm{l}}^{+}$ is more stable than $\mathrm{A}{\mathrm{l}}^{3+}$
2. B.$\mathrm{A}{\mathrm{l}}^{+}$ is more stable than $\mathrm{A}{\mathrm{l}}^{3+}$
3. C.$\mathrm{T}{\mathrm{l}}^{+}$ is more stable than $\mathrm{A}{\mathrm{l}}^{+}$
4. D.$\mathrm{T}{\mathrm{l}}^{3+}$ is more stable than $\mathrm{A}{\mathrm{l}}^{3+}$

Two Faraday of electricity is passed through a solution of $\mathrm{CuS}{\mathrm{O}}_4$. The mass of copper deposited at the cathode is: (at. mass of $\mathrm{Cu}=63.5\mathrm{amu}$)

1. A.$63.5\mathrm{g}$
2. B.$2\mathrm{g}$
3. C.$127\mathrm{g}$
4. D.$0\mathrm{g}$

Resistance of $0.2\mathrm{M}$ solution of an electrolyte is $50\Omega$. The specific conductance of the solution is $1.4\mathrm{S}{\mathrm{m}}^{-1}$. The resistance of $0.5\mathrm{M}$ solution of the same electrolyte is $280\Omega$. The molar conductivity of $0.5\mathrm{M}$ solution of the electrolyte in $\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$ is :

1. A.$5\times 10^3$
2. B.$5\times 10^2$
3. C.$5\times 10^{-4}$
4. D.$5\times 10^{-3}$

Given below are the half-cell reactions: $\mathrm{M}{\mathrm{n}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Mn};{\mathrm{E}}^0=-1.18\mathrm{V}$ $2(\mathrm{M}{\mathrm{n}}^{3+}+{\mathrm{e}}^{-}\to \mathrm{M}{\mathrm{n}}^{2+});{\mathrm{E}}^0=+1.51\mathrm{V}$ The ${\mathrm{E}}^0$ for $3\mathrm{M}{\mathrm{n}}^{2+}\to \mathrm{Mn}+2M{\mathrm{n}}^{3+}$ will be :

1. A.$-0.33\mathrm{V}$; the reaction will not occur
2. B.$-0.33\mathrm{V}$; the reaction will occur
3. C.$-2.69\mathrm{V}$; the reaction will not occur
4. D.$-2.69\mathrm{V}$; the reaction will occur

The equivalent conductance of $\mathrm{NaCl}$ at concentration $\mathrm{C}$ and at infinite dilution are ${\lambda }_C$ and ${\lambda }_{\infty }$, respectively. The correct relationship between ${\lambda }_C$ and ${\lambda }_{\infty }$ is given as: (where the constant $\mathrm{B}$ is positive)

1. A.${\lambda }_C={\lambda }_{\infty }+(B)C$
2. B.${\lambda }_C={\lambda }_{\infty }-(B)C$
3. C.${\lambda }_C={\lambda }_{\infty }-(B)\sqrt{C}$
4. D.${\lambda }_C={\lambda }_{\infty }+(B)\sqrt{C}$

The metal that cannot be obtained by electrolysis of an aqueous solution of its salts is :

1. A.Cu
2. B.Cr
3. C.Ag
4. D.Ca

Given ${\mathrm{E}}_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=0.34\mathrm{V},{\mathrm{E}}_{\mathrm{C}{\mathrm{u}}^{2+}/C{\mathrm{u}}^{+}}^{\circ }=0.15\mathrm{V}$ Standard electrode potential for the half cell $\mathrm{C}{\mathrm{u}}^{+}/Cu$ is

1. A.$0.38\mathrm{V}$
2. B.$0.53\mathrm{V}$
3. C.$0.19\mathrm{V}$
4. D.$0.49\mathrm{V}$

In the electrolysis of alumina to obtain aluminium metal, cryolite is added mainly to

1. A.lower the melting point of alumina
2. B.dissolve alumina in molten cryolite
3. C.remove the impurities of alumina
4. D.increase the electrical conductivity

A battery is constructed of Cr and $\mathrm{N}{\mathrm{a}}_2\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7$. The unbalanced chemical equation when such a battery discharges is following: $$\mathrm{N}{\mathrm{a}}_2\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7+\mathrm{Cr}+{\mathrm{H}}^{+}\to \mathrm{C}{\mathrm{r}}^{3+}+{\mathrm{H}}_2\mathrm{O}+\mathrm{N}{\mathrm{a}}^{+}$$ If one Faraday of electricity is passed through the battery during the charging, the number of moles of $\mathrm{C}{\mathrm{r}}^{3+}$ removed from the solution is

1. A.$\frac{4}{3}$
2. B.$\frac{1}{3}$
3. C.$\frac{3}{3}$
4. D.$\frac{2}{3}$

Given : $E_{F{e}^{3+}/Fe}^o=-0.036\mathrm{V}$; $E_{F{e}^{2+}/Fe}^o=-0.439\mathrm{V}$ The value of standard electrode potential for the change, $\mathrm{F}{\mathrm{e}}^{3+}(\mathrm{aq})+{\mathrm{e}}^{-}\to \mathrm{F}{\mathrm{e}}^{2+}(\mathrm{aq})$ will be

1. A.$-0.072\mathrm{V}$
2. B.$0.385\mathrm{V}$
3. C.$0.770\mathrm{V}$
4. D.$-0.270\mathrm{V}$

Resistance of a conductivity cell filled with a solution of an electrolyte of concentration $0.1\mathrm{M}$ is $100\Omega$. The conductivity of this solution is $1.29\mathrm{S}{\mathrm{m}}^{-1}$. Resistance of the same cell when filled with $0.2\mathrm{M}$ of the same solution is $520\Omega$. The molar conductivity of $0.2\mathrm{M}$ solution of the electrolyte will be

1. A.$124\times 10^{-4}\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$
2. B.$1240\times 10^{-4}\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$
3. C.$1.24\times 10^{-4}\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$
4. D.$12.4\times 10^{-4}\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$

The highest electrical conductivity of the following aqueous solutions is of :

1. A.0.1 M acetic acid
2. B.0.1 M chloroacetic acid
3. C.0.1 M fluoroacetic acid
4. D.0.1 M difluoroacetic acid

Aluminium oxide may be electrolysed at $1000^{\circ }\mathrm{C}$ to furnish aluminium metal (Atomic mass $=27\mathrm{amu}$; 1 Faraday $=96,500\mathrm{Coulombs}$). The cathode reaction is $\mathrm{A}{\mathrm{l}}^{3+}+3{\mathrm{e}}^{-}\to \mathrm{A}{\mathrm{l}}^0$ To prepare $5.12\mathrm{kg}$ of aluminium metal by this method would require

1. A.$5.49\times 10^7\mathrm{C}$ of electricity
2. B.$1.83\times 10^7\mathrm{C}$ of electricity
3. C.$5.49\times 10^4\mathrm{C}$ of electricity
4. D.$5.49\times 10^1\mathrm{C}$ of electricity

During the process of electrolytic refining of copper, some metals present as impurity settle as ‘anode mud’ These are

1. A.Sn and Ag
2. B.Pb and Zn
3. C.Ag and Au
4. D.Fe and Ni

In a hydrogen – oxygen fuel cell, combustion of hydrogen occurs to :

1. A.generate heat
2. B.remove adsorbed oxygen from electrode surfaces
3. C.produce high purity water
4. D.create potential difference between the two electrodes

Consider the following $E^{\circ }$ values $E_{F{e}^{3+}/F{e}^{2+}}^{\circ }$ = 0.77 V; $E_{S{n}^{2+}/Sn}^{\circ }$ = -0.14 V Under standard conditions the potential for the reaction $\mathrm{Sn}(\mathrm{s})+2F{\mathrm{e}}^{3+}(\mathrm{aq})\to 2F{\mathrm{e}}^{2+}(\mathrm{aq})+\mathrm{S}{\mathrm{n}}^{2+}(\mathrm{aq})$ is :

1. A.1.68 V
2. B.0.63 V
3. C.0.91 V
4. D.1.40 V

In a cell that utilises the reaction $\mathrm{Zn}(\mathrm{s})+2{\mathrm{H}}^{+}(\mathrm{aq})\to \mathrm{Z}{\mathrm{n}}^{2+}(\mathrm{aq})+{\mathrm{H}}_2(\mathrm{g})$ addition of ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ to cathode compartment, will

1. A.lower the E and shift equilibrium to the left
2. B.increases the E and shift equilibrium to the left
3. C.increase the E and shift equilibrium to the right
4. D.Lower the E and shift equilibrium to the right

Conductivity (Siemens S) is directly proportional to area of the vessel and the concentration of the solution in it and is inversely proportional to the length of the vessel, then the constant of proportionality is expressed in :

1. A.$\mathrm{Sm}\mathrm{mo}{\mathrm{l}}^{-1}$
2. B.$\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$
3. C.${\mathrm{S}}^{-2}{\mathrm{m}}^2\mathrm{mol}$
4. D.${\mathrm{S}}^2{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-2}$

Which of the following reaction is possible at anode?

1. A.$2C{\mathrm{r}}^{3+}+7{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7^{2-}+14{\mathrm{H}}^{+}$
2. B.${\mathrm{F}}_2\to 2{\mathrm{F}}^{-}$
3. C.$(1/2){\mathrm{O}}_2+2{\mathrm{H}}^{+}\to {\mathrm{H}}_2\mathrm{O}$
4. D.none of these

When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are :

1. A.cathode = pure zinc, anode = pure copper
2. B.cathode = impure sample, anode = pure copper
3. C.cathode = impure zinc, anode = impure sample
4. D.cathode = pure copper, anode = impure sample