Chemistry Reference
In-Depth Information
1
A = 0.001 : B = 0.0001 : C = 0.00001
B
1/e
C
A
Distance
FIGure 7.6
Variation (decrease) in electrostatic potential with distance of separation as a
function of electrolyte concentration (ionic strength).
table 7.1
debye length ([1/
k
] nm) in aqueous
Solutions
Salt concentration molal
1:1
1:2
2:2
0.0001
30.4
17.6
15.2
0.001
9.6
5.55
4.81
0.01
3.04
1.76
1.52
0.1
0.96
0.55
0.48
The data in Table 7.1 show values of D-H radius in various salt concentrations.
The magnitude of 1/κ decreases with
I
and with the number of charges on the added
salt. This means that the thickness of the ion atmosphere around a reference ion will
be much compressed with increasing value of
I
and z
ion
.
A trivalent ion such as Al
3+
will compress the double layer to a greater extent in
comparison with a monovalent ion such as Na
+
. Further, inorganic ions can interact
with the charge surface in one of two distinct ways:
1. Nonspecific ion adsorption, where these ions have no effect on the isoelec-
tric point
2. Specific ion adsorption, which gives rise to change in the value of the
isoelectric-point
Under those conditions, where the magnitude of 1/κ is very small (e.g., in high elec-
trolyte solution), one can write:
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