Q. 24 A5.0( 2 Votes )

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Answer :

a) The cell reaction is :


2Cr + 3Fe2+ 2Cr3+ + 3Fe


To calculate the emf of the cell, we apply the Nernst equation:



Where n = number of electrons involved in the cell reaction


n = 6


E°cell = 0.261 V (given)


Fe2+ = 0.01M , Cr3+ = 0.01M (given)


By putting R = 8.314 JK-1 mole-1


T = 298K


F = 96500 coulombs


We get,



Ecell = 0.2807 V


Thus, the emf of the cell at 298 K is 0.2807 V


b) A is better for coating the surface of iron to prevent corrosion, because its E0 value (-2.3V) is more negative.


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