1.

For Cr_(2)O_(7)^(2-)+14H^(+)+6e^(-)to2Cr^(3+)+7H_(2)O,E^(@)=1.33V At [Cr_(2)O_(7)^(2-)]=4.5 millimole, [Cr^(3+)]=15 millimole, E is 1.067V. Calculate the pH of the solution.

Answer»

Solution :For the GIVEN reaction,
`Cr_(2)O_(7)^(2-)+14H^(+)+6e^(-)to2Cr^(3+)+7H_(2)O`
`E=E^(@)=-(0.0591)/(6)"log"([Cr^(3+)]^(2)[H_(2)O]^(7))/([Cr_(2)O_(7)^(2-)][H^(+)]^(14))`
`1.067=1.33-9.85xx10^(-3)"log"([15xx10^(-3)]^(2)[1]^(7))/([4.5xx10^(-3)][H^(+)]^(14))`
`(-0.263)/(-9.85xx10^(-3))=2LOG(15xx10^(-3))-log(4.5xx10^(-3))-14log(H^(+))`
`26.7=2(-1.82)+2.34+14pH` or `pH=(28)/(14)=2`.


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