For the cell `Pt|H_(2)(g)|"solution"X||KCl("saturated")|Hg_(2)Cl_(2)|Hg|Pt` the observed EMF at `25^(@)C` was `600mV`. When solution X was replaced by a standard phophate buffer with `pH =7.00` , the EMF was `777 mV`. Find the pH of solution X

Options

A. 3
B. 4
C. 5
D. 6

Answer

2

Explanation

`H_(2)rarr2H^(+)+2e^(-)`
`Hg_(2)Cl_(2)+2e^(-)rarr 2Hg+2Cl^(-)`
`bar(H_(2)+Hg_(2)Cl_(2)rarr2H^(+)_2Cl^(-)+2Hg)`
`E_("initial ")=E^(@)+(0.059)/(2)log.(1)/([H^(+)]^(2)[Cl^(-)]^(2))=0.6" "E_("final ")=E^(@)+(0.059)/(2)log.(1)/((10^(-7))^(2)[Cl^(-)]^(2))=0.777`
subtracting we get,
`0.177=0.059log.([H^(+)])/(10^(-7))`
`implies" "([H^(+)])/(10^(-7))=1000" "implies" "[H^(+)]=10^(-4)" "impliespH=4`