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An aqueous solution containing one mole per liter each of Cu(NO3)2, AgNO3, Hg2(NO3)2, Mg(NO3)2 is being electrolyzed by using inert electrodes. The value of standard potentials are
Description: 31626.pngDescription: 31634.png, and
Description: 31643.png
With increasing voltage, the sequence of deposition of metals on the cathodes will be
  1. Ag, Hg, Cu, Mg
  2. Mg, Cu, Hg, Ag
  3. Ag, Hg, Cu
  4. Cu, Hg, Ag
Solution (C)
The metal ions will be preferentially discharged on cathode in the order of their decreasing reduction potentials. The order of deposition of metals will be Ag, Hg, and Cu. Mg will not get deposited because H+ will be preferentially discharged to release H2, and in an aqueous solution, H+ will never get completely consumed during the time period of electrolysis.


The EMF of the cell, Ag | AgCl (saturated solution) || Cl (c1 M) | AgCl | Ag is given by
  1. Description: 31655.png
  2. Description: 31662.png
  3. Description: 31670.png
  4. Description: 31679.png
where KSP is the solubility product of AgCl.
Solution (C)
The given cell can be reduced to
Ag | AgCl (satd. solution) || Ag+Description: 31691.png
The reaction occurring at the two electrodes are as follows:
At anode: Ag h Description: 31701.png
At cathode: Description: 31708.png
Net cell reaction: Description: 31716.png
∴ Description: 31724.png
[Since, it is a concentration cell for which Description: 31734.png
∴ Description: 31745.png
Description: 31753.png


If the pressure of H2 gas is increased from 1 atm to 100 atm keeping H+ concentration constant at 1 M, the change in reduction potential of hydrogen half cell at 25°C will be:
  1. 0.059 V
  2. 0.59 V
  3. 0.0295 V
  4. 0.118 V
Solution (A)
The half cell reaction for hydrogen half cell acting as cathode is
2H+ + 2eh H2
∴ Description: 31764.png
Description: 31773.png
Now, when the pressure of H2 gas is changed to 100 atm without changing [H+], the reduction potential becomes
Description: 31782.png
∴ Change in reduction potential = Description: 31793.png
Description: 31801.png


A galvanic cell is composed of two hydrogen electrodes of which cathode is a standard hydrogen electrode. In which of the following solutions should the other half cell be immersed to get maximum EMF?
  1. 0.1 M C6H5CO2H
  2. 0.1 M CH3CO2H
  3. 0.1 M HCO2H
  4. 0.1 M H2C2O4
Solution (b)
The given galvanic cell is represented as
Pt | H2(1 atm) | Acid (0.1 M) || H+ (1 M) | H2 (1 atm) | Pt
At anode: ½ H2h Description: 31809.png
At cathode: Description: 31817.png
Net cell reaction: Description: 31825.png
This is an electrolyte concentration cell whose Description: 31833.png will be zero. Therefore,
Ecell = 0.059 log Description: 31842.png
The Description: 31852.png is fixed at 1 M, so to get the maximum EMF of the cell, Description: 31860.png should be least. So the acid must be the weakest among all. Order of acidity of the given acids is
H2C2O4> HCO2H > C6H5CO2H > CH3CO2H


An aqueous solution containing Na+, Sn2+, Cl, and Description: 31872.png ions, all at unit concentration, is electrolyzed between a silver anode and a platinum cathode. What changes occur at the electrodes when current is passed through the cell?
Given: Description: 31881.png V,
Description: 31890.png
  1. Sn2+ is reduced and Cl is oxidized
  2. Ag is oxidized and Sn2+ is reduced
  3. Sn2+ is reduced and Sn2+ is oxidized
  4. H+ is reduced and Sn2+ is oxidized
Solution (C)
At anode, either Ag can get oxidized to Ag+ or Sn2+ to Sn4+ or Cl to Cl2 or Description: 31900.png Their corresponding oxidation potential values are –0.799 V, –0.13 V, –1.36 V, and –2 V. From these values, it is evident that at anode Sn2+ would be oxidized first, followed by Ag. At cathode, either Na+ can get reduced to Na or Sn2+ to S or H+ to H2. The reduction potential value for Na+ is highly negative, while for Sn2+|Sn, it is –0.14 V and for Description: 31907.png is –0.413 V.
Thus, Sn2+ will get reduced at cathode followed by H+.

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