Chapter 9

The limiting molar conductivities \(\Lambda^{\circ}\) for \(\mathrm{NaCl}, \mathrm{KBr}\) and \(\mathrm{KCl}\) are 126,152 and \(150 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\) respectively. The \(\Lambda^{\circ}\) for \(\mathrm{NaBr}\) is (a) \(278 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\) (b) \(178 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\) (c) \(128 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\) (d) \(306 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\)

In a cell that utilizes the reaction \(\mathrm{Zn}(\mathrm{s})+2 \mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Zn}^{2+}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})\) Addition of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) to cathode compartment, will (a) lower the \(E\) and shift equilibrium to the right (b) lower the \(E\) and shift the equilibrium to the left (c) increase the \(E\) and shift the equilibrium to the left (d) increase the \(E\) and shift the equilibrium to the right.

For a spontaneous reaction the \(\Delta \mathrm{G}\), equilibrium constant \((\mathrm{K})\) and \(E_{\text {cell }}^{\circ}\) will be respectively \([\mathbf{2 0 0 5}]\) (a) \(-\mathrm{ve},>1,+\mathrm{ve}\) (b) \(+\mathrm{ve},>1,-\mathrm{ve}\) (c) \(-\mathrm{ve},<1,-\mathrm{ve}\) (d) \(-\) ve, \(>1,-\) ve

Aluminium oxide may be electrolysed at \(1000^{\circ} \mathrm{C}\) to furnish aluminium metal (atomic mass \(=27 \mathrm{amu} ; 1\) faraday \(=965000\) coulombs). The cathode reaction is \(\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}\) To prepare \(5.12 \mathrm{~kg}\) of aluminium metal by this method would require [2008] (a) \(5.49 \times 10^{7} \mathrm{C}\) of electricity (b) \(1.83 \times 10^{7} \mathrm{C}\) of electricity (c) \(5.49 \times 10^{4} \mathrm{C}\) of electricity (d) \(5.49 \times 10^{10} \mathrm{C}\) of electricity

The electrical conductivity of the flowing aqueous solutions is highest for (a) \(0.1 \mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}\) (b) \(0.1 \mathrm{M} \mathrm{CH}_{2} \mathrm{FCOOH}\) (c) \(0.1 \mathrm{M} \mathrm{CHF}_{2} \mathrm{COOH}\) (d) \(0.1 \mathrm{M} \mathrm{CH}_{2} \mathrm{ClCOOH}\)

Given the data at \(25^{\circ} \mathrm{C}\). [2006] \(\mathrm{Ag}+\mathrm{I} \stackrel{-}{\longrightarrow} \mathrm{AgI}+\mathrm{e} ; E^{\circ}=0.152 \mathrm{~V}\) \(\mathrm{Ag} \longrightarrow \mathrm{Ag}^{+}+\mathrm{e}^{-} ; E^{\circ}=-0.800 \mathrm{~V}\) What is the value of \(\log \mathrm{K}_{s p}\) for \(\mathrm{Ag}\) I? \((2.303 \mathrm{RT} / F=0.059 \mathrm{~V})\) (a) \(-8.12\) (b) \(+8.612\) (c) \(-37.83\) (d) \(-16.13\)

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 \(0.02 \mathrm{M}\) solution of the electrolyte will be (a) \(124 \times 10^{-4} \mathrm{~S} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\) (b) \(1240 \times 10^{-4} \mathrm{~S} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\) (c) \(1.24 \times 10^{-4} \mathrm{~S} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\) (d) \(12.4 \times 10^{-4} \mathrm{~S} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\)

The equivalent conductances of two strong electrolytes at infinite dilution in \(\mathrm{H}_{2} \mathrm{O}\) (where ions move freely through a solution) at \(25^{\circ} \mathrm{C}\) are given below: [2007] \(\Lambda^{\circ}\left(\mathrm{CH}_{3} \mathrm{COONa}\right)=91.0 \mathrm{~S} \mathrm{~cm}^{2} / \mathrm{equiv}\) \(\Lambda^{\circ}(\mathrm{HCl})=426.2 \mathrm{~S} \mathrm{~cm}^{2} / \mathrm{equiv}\) What additional information/quantity one needs to calculate \(\Lambda^{\circ}\) of an aqueous solution of acetic acid? (a) \(\Lambda^{\circ}\) of \(\mathrm{CH}_{3} \mathrm{COOK}\) (b) The limiting equivalent conductance of \(\mathrm{H}^{+}\left(\lambda^{\circ}\right)\) (c) \(\Lambda^{\circ}\) of chloroacetic acid \(\left(\mathrm{ClCH}_{2} \mathrm{COOH}\right)\) (d) \(\Lambda^{\circ}\) of \(\mathrm{NaCl}\)

The cell \(\mathrm{Zn}\left|\mathrm{Zn}^{2+}(1 \mathrm{M}) \| \mathrm{Cu}^{2+}(1 \mathrm{M})\right| \mathrm{Cu} \mathrm{E}_{\mathrm{cell}}^{\circ}=1.10\) V), was allowed to be completely discharged at 298 \(K\). The relative concentration of \(\mathrm{Zn}^{2+}\) and \(\mathrm{Cu}^{2+}\left(\left[\mathrm{Zn}^{2+}\right] /\right.\) \(\left.\left[\mathrm{Cu}^{2+}\right]\right)\) is [2007] (a) \(37.3\) (b) \(10^{37.3}\) (c) \(9.65 \times 10^{4}\) (d) antilog \((24.08)\)

Given \(\mathrm{E}^{\circ} \mathrm{Cr}^{3+} / \mathrm{Cr}=-0.72 \mathrm{~V}, \mathrm{E}^{\circ} \mathrm{Fe}^{2+} / \mathrm{Fe}=-0.42 \mathrm{~V}\). The potential for the cell \(\mathrm{Cr}\left|\mathrm{Cr}^{3+}(0.1 \mathrm{M}) \| \mathrm{Fe}^{2+}(0.01 \mathrm{M})\right| \mathrm{Fe}\) is (a) \(0.26 \mathrm{~V}\) (b) \(0.399 \mathrm{~V}\) (c) \(-0.339 \mathrm{~V}\) (d) \(-0.26 \mathrm{~V}\)

The reduction potential of hydrogen half-cell will be negative if: (a) \(\mathrm{p}\left(\mathrm{H}_{2}\right)=2 \mathrm{~atm}\) and \(\left[\mathrm{H}^{+}\right]=1.0 \mathrm{M}\) (b) \(\mathrm{p}\left(\mathrm{H}_{2}\right)=1 \mathrm{~atm}\) and \(\left[\mathrm{H}^{+}\right]=1.0 \mathrm{M}\) (c) \(\mathrm{p}\left(\mathrm{H}_{2}\right)=1 \mathrm{~atm}\) and \(\left[\mathrm{H}^{+}\right]=2.0 \mathrm{M}\) (d) \(\mathrm{p}\left(\mathrm{H}_{2}\right)=2 \mathrm{~atm}\) and \(\left[\mathrm{H}^{+}\right]=2.0 \mathrm{M}\)

The standard reduction potentials for \(\mathrm{Zn}^{2+} / \mathrm{Zn}, \mathrm{Ni}^{2+} / \mathrm{Ni}\), and \(\mathrm{Fe}^{2+} / \mathrm{Fe}\) are \(-0.76,-0.23\) and \(-0.44 \mathrm{~V}\) respectively. The reaction \(\mathrm{X}+\mathrm{Y}^{2+} \rightarrow \mathrm{X}^{2+}+\mathrm{Y}\) will be spontaneous when (a) \(\mathrm{X}=\mathrm{Fe}, \mathrm{Y}=\mathrm{Zn}\) (b) \(\mathrm{X}=\mathrm{Ni}, \mathrm{Y}=\mathrm{Zn}\) (c) \(\mathrm{X}=\mathrm{Ni}, \mathrm{Y}=\mathrm{Fe}\) (d) \(\mathrm{X}=\mathrm{Zn}, \mathrm{Y}=\mathrm{Ni}\)

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 \(\mathrm{S} \mathrm{mt}^{2} \mathrm{~mol}^{-1}\) is: (a) \(5 \times 10^{3}\) (b) \(5 \times 10^{2}\) (c) \(5 \times 10^{-4}\) (d) \(5 \times 10^{-3}\)

The equivalent conductance of \(\mathrm{NaCl}\) at concentration \(\mathrm{C}\) and at infinite dilution are \(\lambda_{\mathrm{C}}\) and \(\lambda_{m}\), respectively. The correct relationship between \(\lambda_{\mathrm{C}}\) and \(\lambda_{\infty}\) is given as: (where the constant B is positive) (a) \(\lambda_{\mathrm{C}}=\lambda_{\infty}-(\mathrm{B}) \sqrt{\mathrm{C}}\) (b) \(\lambda_{\mathrm{c}}=\lambda_{\infty}+(\mathrm{B}) \sqrt{\mathrm{C}}\) (c) \(\lambda_{\mathrm{C}}=\lambda_{m}+(\mathrm{B}) \mathrm{C}\) (d) \(\lambda_{\mathrm{C}}=\lambda_{-\infty}-(\mathrm{B}) \mathrm{C}\)

Given below are the half-cell reactions: \(\mathrm{Mn}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Mn} ; \mathrm{E}^{0}=-1.18 \mathrm{~V}\) \(2\left(\mathrm{Mn}^{3+}+\mathrm{e}^{-} \rightarrow \mathrm{Mn}^{2}+\right) ; \mathrm{E}^{\circ}=+1.51 \mathrm{~V}\) The \(\mathrm{E}^{0}\) for \(3 \mathrm{Mn}^{2+} \rightarrow \mathrm{Mn}+2 \mathrm{Mn}^{3+}\) will be: (a) \(-0.33 \mathrm{~V}\); the reaction will not occur (b) \(-0.33 \mathrm{~V}\); the reaction will occur (c) \(-2.69 \mathrm{~V}\); the reaction will not occur (d) \(-2.69 \mathrm{~V}\); the reaction will occur

Two faraday of electricity is passed through a solution of \(\mathrm{CuSO}_{4}\). The mass of copper deposited at the cathode is (at. mass of \(\mathrm{Cu}=63.5\) amu \()\) (a) \(0 \mathrm{~g}\) (b) \(63.5 \mathrm{~g}\) (c) \(2 \mathrm{~g}\) (d) \(127 \mathrm{~g}\)