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151
Criterium 2 (electroneutrality) leads to:
α
-side:
zC
p
+ C
B
(
α
) = C
X
(
β
)
(10.115)
β
-side:
C
B
(
β
) = C
X
(
β
)
(10.116)
37
Using these equations and rearranging (10.117-10.121), one arrives at the
following:
C
B
(
α
) < C
B
(
β
)
(10.121 simplified)
C
X
(
α
) > C
X
(
β
)
(10.122 simplified)
In other words: Counterions are concentrated at the
α
-side, whereas co-ions
are excluded.
3.4.3. A practical example:
Assume we add 0.01 M HCl (instead of NaCl) to the chitosan. Of course the
pH in the system drops to around 2, but HCl also contributes as a salt
because it diffuses freely between the two sides. In this case the co-ion (B) is
H
+
instead of Na
+
. It then follows from eq. 10.121:
C
H+
(
α
) < C
H+
(
β
)
In other words: pH (
α
) > pH (
β
). pH is lower outside the dialysis bag.
If we instead used alginate in the H
+
form (alginic acid) the pH would have
been lower inside the bag.
37 Error in equation number in textbook
NH
3
+
O
HOH
2
C
NH
3
+
HO
O
O
HOH
2
C
HO
O
NH
3
+
O
HOH
2
C
NH
3
+
HO
O
O
HOH
2
C
HO
Cl
-
H
+