Q24 of 50 Page 1

State Faraday’s laws of electrolysis. How much charge in terms of Faraday is required for reduction of 1 mol of Cr2O72- to Cr3+ ?

Faraday's second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.

In the above transformation, Cr [VI] ion gets converted to Cr [III] ion by the following reaction:


Cr+6 + 3e-→ Cr+3


In this reaction only three electrons are involved and hence the charge required in terms of Faraday for reduction of 1 mole is 3F.


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A voltaic cell is set up at 25◦C with the following half cell;

Al / Al3+ (0.001 M) and Ni /Ni2+ (0.50 M)


Calculate the cell voltage. [ E◦ Ni2+/Ni = - 0.25V, E◦Al3+/Al = -1.66V]

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Calculate the potential of hydrogen electrode in contact with a solution whose pH is 10.

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Is the variability in oxidation number of transition elements different from that of non – transition elements? Illustrate with examples.

 25

Give reasons:

(a) d- block elements exhibit more oxidation states than f-block elements.


(b) Orange solution of potassium dichromate turns yellow on adding sodium hydroxide to it.


(c) Zirconium (Z= 40) and Hafnium (Z = 72) have almost similar atomic radii.