Important Questions of Electrochemistry Chemistry | Zigya

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391.

Li occupies a higher position in the electrochemical series of metals as compared to Cu since :

  • the standard reduction potential of Li+/Li is lower than that of Cu2+/Cu

  • the standard reduction potential of Cu2+/Cu is lower than that of Li+/Li

  • the standard oxidation potential of Li+/Li is lower than that of Cu2+/Cu

  • Li is smaller in size as compared to Cu


392.

A hydrogen gas electrode is made by dipping platinum wire in a solution of HCl of pH=10 and by passing hydrogen gas around the platinum wire at 1 atm pressure. The oxidation potential of electrode would be

  • 0.059 V

  • 0.59 V

  • 0.118V

  • 1.18V


393.

At 25°C molar conductance of 0.1 molar aqueous solution of ammonium hydroxide is 9.54 ohm-1cm2 mol-1 and at infinite dilution its molar conductance is 238 ohm-1cm2 mol-1. The degree of ionisation of ammonium hydroxide at the same concentration and temperature is

  • 2.080%

  • 20.800%

  • 4.008%

  • 40.800%


394.

A button cell used in watches functions as following

Zn(s)+Ag2O(s)+H2O (l)  2Ag(s)+Zn2+(aq)+2OH-(aq)IfhalfcellpotentialsareZn2+(aq)+2e-  Zn(s); E° = -0.76 VAg2O(s)+H2O (l)+ 2e- 2Ag(s)+2OH-(aq), E° = 0.34 VThecellpotentialwillbe

  • 1.10 V

  • 0.42 V

  • 0.84 V

  • 1.34 V


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395.

The quantity of electricity needed to separately electrolyze 1 M solution of ZnSO4 , AlCl3 and AgNO3 completely is in the ratio of

  • 2 : 3 : 1

  • 2 : 1 : 1

  • 2 : 1 : 3

  • 2 : 2 : 1


396.

On passing C ampere of current for the time 't' sec through 1 L of 2 (M) CuSO4 solution (atomic weight of Cu= 63. 5), the amount 'm' of Cu (in gram) deposited on cathode will be

  • m = Ct/(63.5 x 96500)

  • m = Ct/(31.25 X 96500)

  • m = (C x 96500)/(31.25 x t)

  • m = (31.25 X C x t)/96500


397.

The two half-cell reactions of an electrochemical cell is given as

Ag+ e- → Ag; EAg+/ Ag° = -0.3995 V

Fe2+ → Fe3+ + e-EFe3+/ Fe2+° = -0.7120 V

The value of cell EMF will be

  • -0.3125 V

  • 0.3125 V

  • 1.114 V

  • -1.114 V


398.

At 25°C, the molar conductance of 0.007 M hydrofluoric acid is 150 mho cm2mol-1 and its Λ°m = 500 cm2mol-1. The value of the dissociation constant of the acid at the given concentration at 25°C is

  • 7 × 10-4 M

  • 7 × 10-5 M

  • 9 × 10-3 M

  • 9 × 10-4 M


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399.

The standard reduction potential Eo for half-reaction are:

Zn  Zn2+ + 2e- ; E° = + 0.76V

Fe  Fe2+ + 2e- ; E° = + 0.41 V

The EMF of the cell reaction

Fe2+ + Zn  Zn2+ + Fe is :

  • - 0.35 V

  • + 0.35 V

  • + 1.17 V

  • - 1.17 V


400.

The formal potential of Fe3+ /Fe2+ in a sulphuric acid and phosphoric acid mixture (E° = +0.61 V) is much lower than the standard potential (E° = +0.77 V). This is due to

  • formation of the species [FeHPO4]+

  • lowering of potential upon complexation

  • formation of the species [FesO4]+

  • high acidity of the medium


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