The concentration of potassium ions inside a biological cell is at least 20 times higher than outside. The resulting potential difference across the cell is important in several processes such as transmission of nerve impulses and maintaining the ion balance. A simplel model for a concentration cell involving a metal `M` is
`M(s)|M^(o+)(aq,0.05 ` molar`)||M^(o+)(aq,1` molar`)|M(s)`
For the abov electrolytic cell, the magnitude of the cell potential is `|E_(cell)|=70mV.`
If the `0.05` moolar solution of `M^(o+)` is replaced by a `0.0025` molar `M^(o+)` solution, then the magnitude of the cell potential would be

Options

A. `35 mV`
B. `70 mV`
C. `140 mV`
D. `700 mV`

Answer

C

Explanation

According to passage,
`0.059 log 20 = 70 mV`
therefore, when `0.05` molar solution of `M_(L)^(+)` is replaced by `0.0025` molar `M_(L)^(+)` solution. Then,
`E_(cell) = -0.059 log.([M_(R)^(+)])/([M_(L)^(+)])`
`= 0.059 log.(1)/(0.0025)`
`= 0.059 log 400 = 0.059 log 20^(2)`
`= 2 xx 0.059 log 20`
`= 2 xx 70 = 140 mV`