Electrochemistry · JEE Main previous year questions

Given at $298\mathrm{K}$ : $${\mathrm{E}}_{\mathrm{F}{\mathrm{e}}^{2+}/Fe}^{\ominus }=\mathrm{X}\mathrm{Volt}$$ $${\mathrm{E}}_{\mathrm{F}{\mathrm{e}}^{3+}/Fe}^{\ominus }=\mathrm{Y}\mathrm{Volt}$$ The ${\mathrm{E}}_{\mathrm{F}{\mathrm{e}}^{3+}/F{\mathrm{e}}^{2+}}^{\ominus }$ in Volt at $298\mathrm{K}$ is given by :

1. A.$2\mathrm{X}-3\mathrm{Y}$
2. B.$3\mathrm{Y}-2\mathrm{X}$
3. C.$3\mathrm{Y}+2\mathrm{X}$
4. D.$\mathrm{Y}+\mathrm{X}$

Consider the following data. $$\begin{array}{cc}\text{Electrolyte}& {\Lambda }_{\mathrm{m}}^{\circ }(\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1})\\ \mathrm{BaC}{\mathrm{l}}_2& x_1\\ {\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4& x_2\\ \mathrm{HCl}& x_3\end{array}$$ $\mathrm{BaS}{\mathrm{O}}_4$ is sparingly soluble in water. If the conductivity of the saturated $\mathrm{BaS}{\mathrm{O}}_4$ solution is $x\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$ then the solubility product of $\mathrm{BaS}{\mathrm{O}}_4$ can be given as (Here ${\Lambda }_{\mathrm{m}}={\Lambda }_{\mathrm{m}}^{\circ }$)

1. A.$\frac{10^6{x}^2}{{\alpha }^2(x_1+x_2-2x_3{)}^2}$
2. B.$\frac{x^2}{(x_1+x_2-2x_3{)}^2}$
3. C.$\frac{{\alpha }^2(x_1+x_2-2x_3{)}^2}{10^6{x}^2}$
4. D.$\frac{x^2}{(x_1+x_2+2x_3{)}^2}$

Given below are two statements: Statement I:Aluminium is more electropositive than thallium as the standard electrode potential value of ${\mathrm{E}}_{\mathrm{A}{\mathrm{l}}^{3+}/Al}^{\circ }$ is negative and ${\mathrm{E}}_{\mathrm{T}{\mathrm{l}}^{3+}/Tl}^{\circ }$ is positive. Statement II: The sum of first three ionization enthalpies of boron is very high when compared to that of aluminium. Due to this reason boron forms covalent compounds only and aluminium forms $\mathrm{A}{\mathrm{l}}^{3+}$ ion. In the light of the above statements, choose the correct answer from the options given below

1. A.Both Statement I and Statement II are true
2. B.Both Statement I and Statement II are false
3. C.Statement I is true but Statement II is false
4. D.Statement I is false but Statement II is true

Given below are two statements: Statement I: Methane can be prepared by decarboxylation of sodium ethanoate, Kolbe's electrolysis of sodium acetate and reaction of $\mathrm{C}{\mathrm{H}}_3\mathrm{MgBr}$ with water. Statement II: Methane cannot be prepared from unsaturated hydrocarbons and by Wurtz reaction. In the light of the above statements, choose the correct answer from the options given below

1. A.Both Statement I and Statement II are true
2. B.Both Statement I and Statement II are false
3. C.Statement I is true but Statement II is false
4. D.Statement I is false but Statement II is true

1. A.
2. B.
3. C.
4. D.

At $298\mathrm{K}$, the molar conductivity of $x\%(w/w)\mathrm{MX}$ solution (aqueous) is $123.5\mathrm{S}\mathrm{c}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$. The conductance of same solution is $1.9\times 10^{-3}\mathrm{S}$. The value of $x$ is ____ $\times 10^{-2}$. (Given : $\text{cell constant}=1.3\mathrm{c}{\mathrm{m}}^{-1}$; $\text{molar mass of MX is }75\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$, $\text{density of aqueous solution of MX at }298\mathrm{K}\text{ is }1.0\mathrm{g}\mathrm{m}{\mathrm{L}}^{-1}$)

The electronegativity of a group 13 element 'E' is same as that of Ge (on Pauling scale and upto one decimal point). The CORRECT statements about ${\mathrm{E}}^{3+}$ are A. It can act as a reducing agent. B. It can act as an oxidizing agent. C. ${\mathrm{E}}^{3+}$ is more stable than ${\mathrm{E}}^{+}$. D. The standard electrode potential value for ${\mathrm{E}}^{3+}/E$ is positive. Choose the correct answer from the options given below:

1. A.A and C Only
2. B.B and C Only
3. C.B and D Only
4. D.A and D Only

An electrochemical cell, consist of the following two redox couples, ${\mathrm{M}}^{x+}(\mathrm{aq})/\mathrm{M}(\mathrm{s})$ $[{\mathrm{E}}_{red}^{\Theta }=+0.15\mathrm{V}]$ and ${\mathrm{Fe}}^{3+}(\mathrm{aq})/\mathrm{Fe}(\mathrm{s})$ $[{\mathrm{E}}_{red}^{\Theta }=-0.036\mathrm{V}]$ . The cell EMF (${\mathrm{E}}_{\mathrm{cell}}$) is recorded to be $0.2057\mathrm{V}$. If the reaction quotient of the electrochemical reaction is found to be $10^{-2}$, then the value of $x$ is ____.(Nearest integer) $[\text{Given : M is a p-block metal and }\frac{2.303\mathrm{RT}}{\mathrm{F}}=0.059\mathrm{V}]$

An electrochemical cell is constructed using half cells in the direction of spontaneous change $\mathrm{Fe}(\mathrm{OH}{)}_2(\mathrm{s})+2{\mathrm{e}}^{-}\to \mathrm{Fe}(\mathrm{s})+2O{\mathrm{H}}^{-}(\mathrm{aq}){\mathrm{E}}^0=-0.88\mathrm{V}$ and $\mathrm{AgBr}(\mathrm{s})+{\mathrm{e}}^{-}\to \mathrm{Ag}(\mathrm{s})+\mathrm{B}{\mathrm{r}}^{-}(\mathrm{aq}){\mathrm{E}}^0=+0.07\mathrm{V}$ Which of the following option is correct ?

1. A.Overall reaction $\mathrm{Fe}(\mathrm{s})+2O{\mathrm{H}}^{-}(\mathrm{aq})+2AgBr(\mathrm{s})\rightleftharpoons \mathrm{Fe}(\mathrm{OH}{)}_2(\mathrm{s})+2Ag(\mathrm{s})+2B{\mathrm{r}}^{-}(\mathrm{aq})$
2. B.${\mathrm{E}}_{\mathrm{cell}}^{\theta }=-0.95\mathrm{V}$
3. C.Fe is reduced in the electrochemical cell
4. D.${\mathrm{E}}_{\mathrm{cell}}^{\theta }$ is an extensive property

Consider the following two half-cell reactions along with the standard reduction potential given : $$\mathrm{C}{\mathrm{O}}_2+6{\mathrm{H}}^{+}+6{\mathrm{e}}^{-}⟶\mathrm{C}{\mathrm{H}}_3\mathrm{OH}+{\mathrm{H}}_2\mathrm{O}{E}_{\mathrm{red}}^{\circ }=0.02\text{ V}$$ $$\frac{1}{2}{\mathrm{O}}_2+2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}⟶{\mathrm{H}}_2\mathrm{O}{E}_{\mathrm{red}}^{\circ }=1.23\text{ V}$$ A fuel cell was set up using the above two reactions such that the cell operates under the standard condition of 1 bar pressure and $298\text{ K}$ temperature. The fuel cell works with $80\%$ efficiency. If the work derived from the cell using $1\text{ mol}$ of $\mathrm{C}{\mathrm{H}}_3\mathrm{OH}$ is used to compress an ideal gas isothermally against a constant pressure of $1\text{ kPa}$, then the change in the volume of the gas, $\Delta V=$ ________ ${\text{m}}^3$. (nearest integer) Given : $F=96500{\text{ C mol}}^{-1}$

Consider the following redox reaction taking place in acidic medium $\mathrm{B}{\mathrm{H}}_4^{-}(\mathrm{aq})+\mathrm{Cl}{\mathrm{O}}_3^{-}(\mathrm{aq})⟶{\mathrm{H}}_2\mathrm{B}{\mathrm{O}}_3^{-}(\mathrm{aq})+\mathrm{C}{\mathrm{l}}^{-}(\mathrm{aq})$ If the Nernst equation for the above balanced reaction is ${\mathrm{E}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cell}}^{\circ }-\frac{\mathrm{RT}}{\mathrm{nF}}\ln \mathrm{Q}$, then the value of $n$ is ____ .(Nearest integer)

A volume of x mL of 5 M ${\text{NaHCO}}_3$ solution was mixed with 10 mL of 2 M ${\text{H}}_2{\text{CO}}_3$ solution to make an electrolytic buffer. If the same buffer was used in the following electrochemical cell to record a cell potential of 235.3 mV, then the value of $\mathbf{x}=$ _____ mL (nearest integer). $\text{Sn(s)}\mid [{\text{Sn(OH)}}_6{]}^{2-}(0.5\text{ M})\mid {\text{HSnO}}_2^{-}(0.05\text{ M})\mid {\text{OH}}^{-}\mid {\text{Bi}}_2{\text{O}}_3\text{(s)}\mid \text{Bi(s)}$ Consider up to one place of decimal for intermediate calculations $$\left[\text{Given: }\begin{array}{rl}& E_{[{\text{Sn(OH)}}_6{]}^{2-}\mid {\text{HSnO}}_2^{-}}^{\circ }=-0.9\text{V}\\ & E_{{\text{Bi}}_2{\text{O}}_3\mid \text{Bi}}^{\circ }=-0.44\text{ V}\\ & {\text{pK}}_{\text{a}({\text{H}}_2{\text{CO}}_3)}=6.11\\ & \frac{2.303\text{RT}}{\text{F}}=0.059\text{ V}\\ & \text{Antilog}(1.29)=19.5\end{array}\right]$$

For strong electrolyte ${\Lambda }_m$ increases slowly with dilution and can be represented by the equation ${\Lambda }_m={\Lambda }_m^{\circ }-A{c}^{1/2}$ Molar conductivity values of the solutions of strong electrolyte AB at 18°C are given below : $$\begin{array}{lcccc}\mathbf{c}{\text{ [mol L}}^{-1}\text{]}& 0.04& 0.09& 0.16& 0.25\\ {\Lambda }_m{\text{ [S cm}}^2{\text{ mol}}^{-1}\text{]}& 96.1& 95.7& 95.3& 94.9\end{array}$$ The value of constant A based on the above data [in ${\text{S cm}}^2{\text{ mol}}^{-1}/(\text{mol/L}{)}^{1/2}$] unit is ________.

Electricity is passed through an acidic solution of $\mathrm{C}{\mathrm{u}}^{2+}$ till all the $\mathrm{C}{\mathrm{u}}^{2+}$ was exhausted, leading to the deposition of $300\mathrm{mg}$ of $\mathrm{Cu}$ metal. However, a current of $600\mathrm{mA}$ was continued to pass through the same solution for another $28\text{minutes}$ by keeping the total volume of the solution fixed at $200\mathrm{mL}$ . The total volume of oxygen evolved at STP during the entire process is ____ $\mathrm{mL}$ . (Nearest integer) [Given: $\mathrm{C}{\mathrm{u}}^{2+}(\mathrm{aq})+2{\mathrm{e}}^{-}\to \mathrm{Cu}(\mathrm{s}){\mathrm{E}}_{\mathrm{red}}^{\mathrm{o}}=+0.34\mathrm{V}$ ${\mathrm{O}}_2(\mathrm{g})+4{\mathrm{H}}^{+}+4{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2\mathrm{O}{\mathrm{E}}_{\mathrm{red}}^{\mathrm{o}}=+1.23\mathrm{V}$ Molar mass of $\mathrm{Cu}=63.54\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$ Molar mass of ${\mathrm{O}}_2=32\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$ Faraday Constant $=96500\mathrm{Cmo}{\mathrm{l}}^{-1}$ Molar volume at $\mathrm{STP}=22.4\mathrm{L}$ ]

In the given electrochemical cell, $\mathrm{Ag}(\mathrm{s})|AgCl(\mathrm{s})|FeC{\mathrm{l}}_2(\mathrm{aq}),\mathrm{FeC}{\mathrm{l}}_3(\mathrm{aq})\mid \mathrm{Pt}(\mathrm{s})$ at 298 K , the cell potential ( $E_{\mathrm{cell}}$ ) will increase when : A. Concentration of ${\mathrm{Fe}}^{2+}$ is increased. B. Concentration of ${\mathrm{Fe}}^{3+}$ is decreased. C. Concentration of ${\mathrm{Fe}}^{2+}$ is decreased. D. Concentration of ${\mathrm{Fe}}^{3+}$ is increased. E. Concentration of ${\mathrm{Cl}}^{-}$ is increased. Choose the correct answer from the options given below :

1. A.C, D and E Only
2. B.A and B Only
3. C.B Only
4. D.A and E Only

1. A.If $c_1$ is present at anode, then $c_1>c_2$.
2. B.If $c_1$ is present at cathode, then $c_1>c_2$.
3. C.If $c_1$ is present at cathode, then $c_1<c_2$.
4. D.If $c_1$ is present at anode, then $c_1=c_2$.

Consider the following electrochemical cell at 298 K $\mathrm{Pt}\left|\mathrm{HSn}{\mathrm{O}}_2^{-}(\mathrm{aq})\right|\mathrm{Sn}(\mathrm{OH}{)}_6{}^{2-}(\mathrm{aq})\left|\mathrm{O}{\mathrm{H}}^{-}(\mathrm{aq})\right|\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3(\mathrm{s})\mid \mathrm{Bi}(\mathrm{s})$. If the reaction quotient at a given time is $10^6$, then the cell EMF $\left({\mathrm{E}}_{\mathrm{cell}}\right)$ is ____ $\times 10^{-1}\mathrm{V}$ (Nearest integer). Given the standard half-cell reduction potential as ${\mathrm{E}}_{\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3/Bi,\mathrm{O}{\mathrm{H}}^{-}}^{\circ }=-0.44\mathrm{V}$ and ${\mathrm{E}}_{\mathrm{Sn}(\mathrm{OH}{)}_6^{2-}/HSn{\mathrm{O}}_2^{-},\mathrm{O}{\mathrm{H}}^{-}}^{\circ }=-0.90\mathrm{V}$

The pH and conductance of a weak acid $(\mathrm{HX})$ was found to be 5 and $4\times 10^{-5}\mathrm{S}$, respectively. The conductance was measured under standard condition using a cell where the electrode plates having a surface area of $1\mathrm{c}{\mathrm{m}}^2$ were at a distance of 15 cm apart. The value of the limiting molar conductivity is ____ $\mathrm{S}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$. (nearest integer) (Given : degree of dissociation of the weak acid $(\alpha )\ll 1$)

On charging the lead storage battery, the oxidation state of lead changes from $x_1$ to $y_1$ at the anode and from $x_2$ to $y_2$ at the cathode. The values of $x_1,y_1,x_2,y_2$ are respectively :

1. A.$0,+2,+4,+2$
2. B.$+2,0,0,+4$
3. C.$+4,+2,0,+2$
4. D.$+2,0,+2,+4$

Correct order of limiting molar conductivity for cations in water at $298\mathrm{K}$ is :

1. A.${\mathrm{H}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{Ca}}^{2+}>{\mathrm{Mg}}^{2+}$
2. B.${\mathrm{H}}^{+}>{\mathrm{Ca}}^{2+}>{\mathrm{Mg}}^{2+}>{\mathrm{K}}^{+}>{\mathrm{Na}}^{+}$
3. C.${\mathrm{Mg}}^{2+}>{\mathrm{H}}^{+}>{\mathrm{Ca}}^{2+}>{\mathrm{K}}^{+}>{\mathrm{Na}}^{+}$
4. D.${\mathrm{H}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{Ca}}^{2+}>{\mathrm{Mg}}^{2+}>{\mathrm{K}}^{+}$

The standard cell potential $\left({\mathrm{E}}_{\mathrm{cell}}^{\ominus }\right)$ of a fuel cell based on the oxidation of methanol in air that has been used to power television relay station is measured as $1.21\mathrm{V}$. The standard half cell reduction potential for ${\mathrm{O}}_2$ $\left({\mathrm{E}}_{{\mathrm{O}}_2/{\mathrm{H}}_2\mathrm{O}}^{\circ }\right)$ is $1.229\mathrm{V}$. Choose the correct statement :

1. A.Reactants are fed at one go to each electrode.
2. B.Oxygen is formed at the anode.
3. C.The standard half cell reduction potential for the reduction of ${\mathrm{CO}}_2$ $\left({\mathrm{E}}_{{\mathrm{CO}}_2/{\mathrm{CH}}_3\mathrm{OH}}^{\circ }\right)$ is $19\mathrm{mV}$
4. D.Reduction of methanol takes place at the cathode.

1. A.The concentration of ${\mathrm{CH}}_3\mathrm{COOH}$ in the original mixture is $0.005\mathrm{M}$
2. B.The concentration of $\mathrm{HCl}$ in the original mixture is $0.005\mathrm{M}$
3. C.${\mathrm{CH}}_3\mathrm{COOH}$ is neutralised first followed by neutralisation of $\mathrm{HCl}$
4. D.Point ' C ' indicates the complete neutralisation of $\mathrm{HCl}$

$0.2\%(w/v)$ solution of $\mathrm{NaOH}$ is measured to have resistivity $870.0\mathrm{m\Omega }\mathrm{m}$. The molar conductivity of the solution will be ____ $\times 10^2\mathrm{mS}\mathrm{d}{\mathrm{m}}^2\mathrm{mo}{\mathrm{l}}^{-1}$. (Nearest integer)

Match List - I with List - II : $$\begin{array}{ll}\text{List - I (Applications)}& \text{List - II (Batteries/Cell)}\\ \text{(A) Transistors}& \text{(I) Anode - Zn/Hg; Cathode - HgO + C}\\ \text{(B) Hearing aids}& \text{(II) Hydrogen fuel cell}\\ \text{(C) Inverters}& \text{(III) Anode - Zn; Cathode - Carbon}\\ \text{(D) Apollo space ship}& \text{(IV) Anode - Pb; Cathode - Pb | }\mathrm{Pb}{\mathrm{O}}_2\end{array}$$ Choose the correct answer from the options given below :

1. A.(A)-(III), (B)-(I), (C)-(IV), (D)-(II)
2. B.(A)-(II), (B)-(III), (C)-(IV), (D)-(I)
3. C.(A)-(IV), (B)-(III), (C)-(II), (D)-(I)
4. D.(A)-(III), (B)-(II), (C)-(IV), (D)-(I)