Redox Reactions And Electrochemistry Ques 738
Question: For the cell $ Pt|H_2(g)| $ solution $ X||KCI $ (saturated) $ |Hg_2Cl_2|Hg|,Pt $ the observed EMF at $ 25{}^\circ C $ was $ 600mV. $ When solution X was replaced by a standard phosphate buffer with $ pH=7.00, $ the EMF was $ 777mV $ . Find the pH of solution X.
Options:
A) 3
B) 4
C) 5
D) 6
Show Answer
Answer:
Correct Answer: B
Solution:
[b] $ H_2\xrightarrow{{}}2{H^{+}}+2{e^{-}} $ $ \frac{Hg_2Cl_2+2{e^{-}}\xrightarrow{{}}2Hg+2C{l^{-}}}{H_2+Hg_2Cl_2\xrightarrow{{}}2{H^{+}}+2C{l^{-}}+2Hg} $ $ E_{initial}=E{}^\circ +\frac{0.059}{2}\log \frac{1}{{{[{H^{+}}]}^{2}},{{[C{l^{-}}]}^{2}}}=0.6 $ $ {E_{final}}=E{}^\circ +\frac{0.059}{2}\log \frac{1}{{{({10^{-7}})}^{2}},{{[C{l^{-}}]}^{2}}}=0.777 $ subtracting we get $ 0.177=0.059\log \frac{[{H^{+}}]}{{10^{-7}}} $
$ \Rightarrow $ $ \frac{[{H^{+}}]}{{10^{-7}}}=1000 $
$ \Rightarrow $ $ [{H^{+}}]={10^{-4}} $
$ \Rightarrow pH=4. $
