AMMONIA User Manual
AMMONIA_User 9/09
6
The electrolyte has a relatively high concentration of ammonium chloride, so the concentration of ammonium ions
in the thin electrolyte layer may be regarded as constant if a small amount of NH
3
permeates the membrane and
NH
4
+
is formed in accordance with the equation given above. As a result, the concentration of ammonium ions can
be included in the equilibrium constant K´.
K´ = [OH
-
] / [NH3]
or
[OH
-
] ~ [NH3]
(3)
Applying the Nernst equation thus results in the following dependency:
E = E
0
- S log [NH3]
(4)
E = electrode potential
E
0
= standard electrode potential
S = slope, f (T)
pH dependence
In accordance with the above-mentioned reaction equation (Equation 1), ammonia (NH
3
) in an aqueous solution is in
a pH-dependent equilibrium with ammonium ions (NH
4+
). This dependence is shown in Figure 3.
Fig. 3: pH dependence of the equilibrium between ammonia and ammonium ions