Physical Chemistry 2.pdf - OER@AVU - African Virtual University

sp =
c
p
k
African Virtual University
s
2
= k1
+ k2c
+ k3c
sp
(2.11)
c = k
c
The value of ç s p can be determined by extrapolating to infinite dilution a plot of ç s p
against c. c
c
sp a 2
[ ]
= KM
Approximate
= k1
+ k
molar 2c
+ k3c
c
masses are easily determined using the Mark-Houwink equation
[ ]
= KM
a
(2.12)
The constants K and a are characteristic of a particular polymer-solvent system.
(e) Electrical particles. Colloidal particles are affected by charges adsorbed on the
surface of the particles. Charges are adsorbed when particles are dispersed in a liquid
medium, an electric double layer forms around the particle as shown in the Figure 2.4
below. Such a system can be attained by adding a salt, for example potassium iodide,
to a dilute solution. The stability of a colloidal system is affected by the presence and
magnitude of a charge on a particle. The presence of a charge on particle creates a
shield that prevents coalescence of the particles via mutual repulsion. Lyophobic sols
are thermodynamically unstable, the presence of electrical charges impart stability
due to repulsions that prevent coagulation.
Particle surface
+
+ − +
+ +
+
+
+
+
+
−
+
+
+ −
+
+ −
Fixed portion of
the double layer
Mobile or diffuse portion
+
+
+
Bulk solution
+ + + + +
+ + + + +
+ + + + +
+ + +
Figure 2.4 Illustration of double layer formation in the vicinity of a colloidal
particle. Diagram shows the position of the particle, diffuse
portion and the bulk solution.