Consider the above electrochemical cell where a metal electrode (M) is undergoing redox reaction by forming 
. The cation 
is present in two different concentrations 
and 
as shown above. Which of the following statement is correct for generating a positive cell potential?
is present at cathode, then 
. 
is present at anode, then 
. 
is present at cathode, then 
. 
is present at anode, then 
.
Text Solution
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The given setup is a concentration cell with identical electrodes ( 
) and different electrolyte concentrations ( 
and 
).
For a concentration cell, the standard cell potential 
.
The cell reactions are:
Anode: 
Cathode: 
Net reaction: 
Using the Nernst equation at 298 K :
For a positive cell potential 
, the term 
must be negative.
This requires 
, which means 
.
If 
is present at the cathode and 
is at the anode, then for 
, we must have 
.
Checking the options:
If 
is at cathode, 
(Incorrect)
If 
is at anode, 
(Incorrect, would require 
)
If 
is at cathode, 
(Correct)
If 
is at anode, 
(Incorrect, 
would be zero)
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