Eh is a m
easure of the redox
(oxidat ion
-reduc ti
on) stat e of a solut ion or,
more exact ly, i ts
solut es. Eh is a
measur
ement of elec trical pot ent ial and
t hus co
mmonly expressed in
volts.
Val
ues
of Eh in nat ure range
from -0.6
t o +0.9V,
wit h 0.0 charact erizing a solut ion wit h no
drive t o ei t
her oxidize or reduce. Accurat e
measur
ement of Eh is much more difficult
t han t h
at of pH, because measurement of
Eh requires
e
quilibrat ion wit h many so
lut es
and ev
en so
lids.
Unlike pH, Eh is not a measure of
conc
ent rat ion of somet hing, and use of the
relat ed paramet er pE = (-logae-) requires
recognit ion t hat pE is a complet ely
t heoret ical expr
ession, ignoring t he realit y
t hat t he co
ncent rat ion of elect rons in a
solut ion
is always ze
ro. pE = Eh ÷ 0.05916.