Question #6e2b5

1 Answer
Mar 5, 2016

Answer:

Depends on the species at hand,

Explanation:

Species like

#Zn^(+2) + 2e^(-) rarr Zn^(0)#
#S_2O_8^-2 + 2e^(-) rarr 2SO_4^-2#

Aren't really affected by the pH, although species like

#8 H^+ +MnO_4^− + 5 e^(−) rarr Mn^(2+) + 4 H_2O#
#2 Cr^(3+) + 21 H_2O rarr Cr_2O_7^-2 + 14H_3O^+ +6e^- #
#2H^+ + 2e^(-) rarr H_2#

Are influenced by the pH, since the pH will influence the reduction potential, which will influence the #DeltaE# of the system.

In general, if we have species that

#aA + b H^+ + n e^(-) rarr c B + k H_2O#

(Having a semirreaction that won't necessarily be real, just for explanation purposes, assuming of course this is a balanced equation as well as remembering we always write these equations as reductions and not oxidations)

The reduction potential (at standard temperature and pressure) will be given by

#E = E^0 - 59.15/n*log([B]^c/([H^+]^b[A]^a))#

(For units in milivolts, if you'd rather work with volts, just use #0.05915#)

From there all you need to do to see how the pH wil affect the reaction is plug in #10^(-pH)# in the place of #[H^+]# or #[H_3O^+]# depending on the author and go on your merry way.