Physical Chemistry

CSIR NET Chemical Science — Electrochemistry previous year questions

30 questions · 2011–2021 · all with verified answer · last checked 2026-11-06

Q1 · June 2021 · 2 marks

For the cell Cd | \mathrm{CdCl_2} || AgCl | Ag; E^\circ_{\text{cell}} = 0.675\ \mathrm{V} and dE^\circ_{\text{cell}}/dT = -6.5 \times 10^{-4}\ \mathrm{V\,K^{-1}} at 27°C. The \Delta H (\mathrm{kJ\,mol^{-1}}) value for the reaction \mathrm{Cd + 2AgCl \rightarrow 2Ag + CdCl_2} is closest to

(a) -168
(b) -123
(c) -95
(d) -234

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Answer: (a)

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Q2 · June 2021 · 2 marks

For weak electrolyte like acetic acid, the relation among conductance (\lambda), equilibrium constant (K) and concentration (C) can be expressed as: (\lambda_o is conductance at infinite dilution)

(a) \frac{1}{\lambda} = \frac{1}{\lambda^o} - \frac{C\lambda}{k\lambda^o}
(b) \frac{1}{\lambda} = \frac{1}{\lambda^o} + \frac{C\lambda}{K\lambda^o}
(c) \frac{1}{\lambda} = \frac{1}{\lambda^o} + \frac{C\lambda}{K\lambda^{o2}}
(d) \frac{1}{\lambda} = \frac{C\lambda}{K\lambda^{o2}}

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Answer: (b)

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Q3 · June 2021 · 2 marks

The amount of \mathrm{Ba(NO_3)_2} (molecular weight 261.32 amu) required to be added to 500 g of a 0.11 mol \mathrm{kg^{-1}} solution of \mathrm{KNO_3} in order to raise its ionic strength to 1.00 is approximately

(a) 38.8 g
(b) 19.4 g
(c) 76.2 g
(d) 126.5 g

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Answer: (a)

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Q4 · June 2019 · 2 marks

The mobility of a divalent cation in water is 8 \times 10^{-8} \mathrm{~m}^{2} \mathrm{~V}^{-1} \mathrm{~S}^{-1}. The effective radius of the ion is (viscosity of water =1 \mathrm{cP} ; \mathrm{e}=1.6 \times 10^{-19} \mathrm{C} )

(a) 106 pm
(b) 212 pm
(c) 424 pm
(d) 318 pm

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Answer: (b)

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Q5 · June 2019 · 2 marks

If the over potential of an electrolysis process is increased from 0.5\mathrm{V} to 0.6\mathrm{V}, then the ratio of current densities \left(\ln\frac{\mathrm{J}_{0.6}}{\mathrm{J}_{0.5}}\right) of the electrolysis will be equal to (given transfer coefficient =0.5)

(a) 0.5\frac{\mathrm{F}}{\mathrm{RT}}
(b) 0.05\frac{\mathrm{F}}{\mathrm{RT}}
(c) 0.1\frac{\mathrm{F}}{\mathrm{RT}}
(d) 0.01\frac{\mathrm{F}}{\mathrm{RT}}

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Answer: (b)

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Q6 · Dec 2019 · 2 marks

The E_0(\mathrm{M^+/M}) of the cell, SHE \| MX | M can be obtained from the plot of (E_{cell} is the cell potential and m is molality of ideal dilute solution of MX)

(a) E_{cell} vs (T\log m)
(b) E_{cell} vs \left(\frac{1}{T}\log m\right)
(c) E_{cell} vs T\sqrt{m}
(d) E_{cell} vs \left(\frac{\sqrt{m}}{T}\right)

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Answer: (a)

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Q7 · Dec 2018 · 2 marks

The standard free energy of the reaction

\mathrm{AgBr}(s) \rightarrow \mathrm{Ag^+}(aq) + \mathrm{Br^-}(aq)

Is closest to.

\left[E^o(\mathrm{AgBr/Ag, Br^-}) = 0.07\,\mathrm{V};\ E^o(\mathrm{Ag/Ag^+}) = 0.80\,\mathrm{V};\ F = 96500\,\mathrm{C\,mol^{-1}}\right]

(a) 7\,\mathrm{kJ\,mol^{-1}}
(b) 70\,\mathrm{J\,mol^{-1}}
(c) 70\,\mathrm{kJ\,mol^{-1}}
(d) 7\,\mathrm{J\,mol^{-1}}

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Answer: (c)

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Q8 · June 2017 · 2 marks

The electrochemical cell potential (E), after the reactants and products reach equilibrium, is ( \mathrm{E}^{0} is the standard cell potential and n is the number of electrons involved)

(a) E=E^{o}+\frac{n F}{R T}
(b) E=E^{o}-\frac{R T}{n F}
(c) E=E^{o}
(d) E=0

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Answer: (d)

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Q9 · June 2017 · 2 marks

The specific conductance of a solution is 0.176 \Omega^{-1} \mathrm{~cm}^{-1}. If the cell constant is 0.255 \mathrm{~cm}^{-1}, the conductance ( \Omega^{-1} ) of that solution is

(a) 1.449
(b) 0.690
(c) 0.045
(d) 0.431

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Answer: (b)

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Q10 · June 2017 · 2 marks

The standard cell potential for the reaction \mathrm{Zn(s) + Cu^{2+}(aq) \Leftrightarrow Zn^{2+}(aq) + Cu(s)} is +1.10 V. The Gibbs free energy change during the reaction is (F = 96500 coulomb \mathrm{mol^{-1}})

(a) -21.2 \mathrm{kJ\,mol^{-1}}
(b) +212 \mathrm{kJ\,mol^{-1}}
(c) -212 \mathrm{kJ\,mol^{-1}}
(d) -212 \mathrm{J\,mol^{-1}}

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Answer: (c)

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Q11 · Dec 2016 · 2 marks

Given (i) \mathrm{Zn + 4NH_3 \rightarrow Zn(NH_3)_4^{2+} + 2e},

E^{o} = 1.03\ \mathrm{V}

(ii) \mathrm{Zn \rightarrow Zn^{+2} + 2e},

E^{0} = 0.763\ \mathrm{V}

the formation constant of the complex \mathrm{Zn(NH_3)_4^{2+}} is approximately

(a) 1 \times 10^{5}
(b) 1 \times 10^{7}
(c) 1 \times 10^{9}
(d) 1 \times 10^{12}

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Answer: (c)

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Q12 · Dec 2016 · 2 marks

If the specific conductances of a sparingly soluble (1:1) salt \left(\mathrm{MW}=200 \mathrm{~g} \mathrm{~mol}^{-1}\right) in its saturated aqueous solution at 25^{\circ} \mathrm{C} and that of water are 1.5 \times 10^{-3} \mathrm{ohm}^{-1} \mathrm{dm}^{-1} and 1.5 \times 10^{-5} \mathrm{ohm}^{-1} \mathrm{dm}^{-1}, respectively, and the ionic conductances for its cation and anion at infinite dilution are 0.485 and 1.0 ohm { }^{-1} \mathrm{dm}^{2} \mathrm{~mol}^{-1}, respectively, the solubility (in \mathrm{g} \mathrm{L}^{-1} ) of the salt in water at 25^{\circ} \mathrm{C} is

(a) 1 \times 10^{-6}
(b) 1 \times 10^{-3}
(c) 2 \times 10^{-1}
(d) 2 \times 10^{-4}

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Answer: (c)

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Q13 · June 2016 · 2 marks

In a potentiometric titration, the end point is characterised by

(a) \frac{dE}{dV} = 0;\ \frac{d^2E}{d^2V} = 0
(b) \frac{dE}{dV} \neq 0;\ \frac{d^2E}{d^2V} = 0
(c) \frac{dE}{dV} = 0;\ \frac{d^2E}{d^2V} \neq 0
(d) \frac{dE}{dV} \neq 0;\ \frac{d^2E}{d^2V} \neq 0

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Answer: (b)

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Q14 · June 2016 · 2 marks

The standard electrode potential E_0 at a fixed temperature and in a given medium is dependent on

(a) only the electrode composition
(b) the electrode composition and the extent of the reaction
(c) the extent of the electrode reaction only
(d) the electrode reaction and the electrode composition

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Answer: (d)

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Q15 · June 2016 · 2 marks

Two aqueous 1 : 1 electrolyte systems A and B are at different temperatures T_A and T_B and C_A and C_B concentrations, respectively. Their Debye lengths will be equal if

(c) T_A = \sqrt{2}\,T_B and C_A = 2C_B
(a) T_A = 2T_B and C_A = 2C_B
(b) T_A = 2T_B and C_A = C_{B/2}
(d) T_A = 2T_B and C_A = \sqrt{2}\,C_B

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Answer: (a)

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Q16 · Dec 2016 · 2 marks

The ionic strength of a solution containing 0.008 M \mathrm{AlCl_3} and 0.005 M KCl is

(a) 0.134 M
(b) 0.053 M
(c) 0.106 M
(d) 0.086 M

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Answer: (b)

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Q17 · Dec 2016 · 2 marks

Given : (i) \mathrm{Zn + 4NH_3 \rightarrow Zn(NH_3)_4^{2+} + 2e}, E^0 = 1.03 V (ii) \mathrm{Zn \rightarrow Zn^{+2} + 2e}, E^\circ = 0.763 V the formation of the complex \mathrm{Zn(NH_3)_4^{2+}} is approximately

(a) 1 \times 10^{5}
(b) 1 \times 10^{7}
(c) 1 \times 10^{9}
(d) 1 \times 10^{12}

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Answer: (c)

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Q18 · June 2015 · 2 marks

The temperature-dependence of an electrochemical cell potential is

(a) \frac{\Delta G}{nFT}
(b) \frac{\Delta H}{nF}
(c) \frac{\Delta S}{nF}
(d) \frac{\Delta S}{nFT}

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Answer: (c)

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Q19 · Dec 2015 · 2 marks

Given that E^o(\mathrm{Cl_2/Cl^-}) = 1.35\,\mathrm{V} and K_{sp}(\mathrm{AgCl}) = 10^{-10} at 25°C, E_o corresponding to the electrode reaction \frac{1}{2}\mathrm{Cl_2}(g) + \mathrm{Ag^+}(\text{Soln.}) + e^- \rightarrow \mathrm{AgCl}(s) is \left[\frac{2.303RT}{F} = 0.06\,\mathrm{V}\right]

(a) 0.75 V
(b) 1.05 V
(c) 1.65 V
(d) 1.95 V

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Answer: (d)

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Q20 · Dec 2015 · 2 marks

The standard EMF of the cell \mathrm{Pt, H_2(g)\,|\,HCl(soln.)\,|\,AgCl(s), Ag(s)}

(a) increases with T
(b) decreases with T
(c) remains unchanged with T
(d) decreases with [HCl]

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Answer: (b)

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Q21 · June 2015 · 2 marks

The temperature-dependence of an electrochemical cell potential is

(a) \frac{\Delta \mathrm{G}}{\mathrm{nFT}}
(b) \frac{\Delta \mathrm{H}}{\mathrm{nF}}
(c) \frac{\Delta \mathrm{S}}{\mathrm{nF}}
(d) \frac{\Delta \mathrm{S}}{\mathrm{nFT}}

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Answer: (c)

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Q22 · Dec 2015 · 2 marks

The concentration of a \mathrm{MgSO_4} solution having the same ionic strength as that of a 0.1 M \mathrm{Na_2SO_4} solution is

(a) 0.05 M
(b) 0.067 M
(c) 0.075 M
(d) 0.133 M

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Answer: (c)

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Q23 · June 2014 · 2 marks

Solutions of three electrolytes have the same ionic strength and different dielectric constants as 4, 25 and 81. The corresponding relative magnitude of Debye-Huckel screening, lengths of the three solutions are

(a) 4, 25 and 81
(b) 2, 5 and 9
(c) 1/2, 1/5 and 1/9
(d) 1, 1 and 1

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Answer: (b)

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Q24 · Dec 2013 · 2 marks

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Answer: (d)

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Q25 · June 2013 · 2 marks

If the concentration (c) is increased to 4 times its original value (c), the change in molar conductivity for strong electrolytes is (where b is Kohlrausch constant)

(a) 0
(b) b\sqrt{c}
(c) 2b\sqrt{c}
(d) 4b\sqrt{c}

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Answer: (b)

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Q26 · Dec 2013 · 2 marks

In a potentiometric titration, the end point is obtained by observing

(a) change in colour
(b) jump in potential
(c) increase in current
(d) increase in turbidity

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Answer: (b)

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Q27 · Dec 2013 · 2 marks

Electrolysis of an aqueous solution of 1.0 M NaOH results in

(a) Na at the cathode and \mathrm{O}_{2} at the anode.
(b) \mathrm{H}_{2} at the cathode and \mathrm{O}_{2} at the anode.
(c) Na and \mathrm{H}_{2} at the cathode, and \mathrm{O}_{2} at the anode.
(d) \mathrm{O}_{2} at the cathode and \mathrm{H}_{2} at the anode.

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Answer: (b)

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Q28 · Dec 2013 · 2 marks

The limiting molar conductivities of NaCl, NaI and RbI are 12.7, 10.8 and 9.1 \mathrm{mS\,m^2\,mol^{-1}}, respectively. The limiting molar conductivity of RbCl would be

(a) 32.6 \mathrm{mS\,m^2\,mol^{-1}}
(b) 7.2 \mathrm{mS\,m^2\,mol^{-1}}
(c) 14.4 \mathrm{mS\,m^2\,mol^{-1}}
(d) 11.0 \mathrm{mS\,m^2\,mol^{-1}}

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Answer: (d)

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Q29 · Dec 2012 · 2 marks

The potential in Debye-Hückel theory is proportional to

(a) 1/\kappa r
(b) \exp[-\kappa r]
(c) \exp[-\kappa r]/r
(d) \kappa r

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Answer: (c)

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Q30 · Dec 2012 · 2 marks

The potential in Debye-Huckel theory is proportional to

(a) 1/\kappa r
(b) \exp[-\kappa r]
(c) \exp[-\kappa r]/r
(d) \kappa r

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Answer: (c)

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