Page 15 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202
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Letter in brackets represents activity
• E0 equals to half-cell potential WHEN the log term is zero
• WHEN all reactants and products are in their standard state
activities, the log term is zero
Typical half-cell reactions / Nernst Expressions
1) Zn2+ + 2e– Zn(s)
No term of elemental zinc is included because it is pure solid
0.059 1
[Zn2+]
E = E0 – log
2
2) 2H+ + 2e– H2(g)
PH2 Is the partial pressure of H2 in atm.
0.059 PH2
E = E0 – log
2 [H+] 2
3) MnO4– + 5e– + 8H+ Mn2+ + 4 H2O
The potential depends on the conc of Mn species and the pH
0.059 [Mn2+]
[MnO4–] [H+]8
E = E0 – log
5
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