Page 295 - Introduction to Colloid and Surface Chemistry

284 Problems
3 3
aqueous solutions at 25°C: (a) 0.1 fflol din" KCl, (6) 0.001 mol dm™
3 3
KCI, (c) 0.001 mol dm" K 2SO 4, (d) 0.001 mol dm" MgCl 2.
29. Electrokinetic measurements at 25°C on silver iodide in 10~ 3
3
mol dm" aqueous potassium nitrate give d£/d(pAg) = — 35 mV at
the zero point of charge. Assuming no specific adsorption of K + or
NO 3 ions and no potential drop within the solid, estimate the
capacity of the inner part of the electric double layer. Taking the
thickness of the inner part of the double layer to be 0.4 nm, what
value for the dielectric constant near to the interface does this imply?
Comment on the result.

30. In a microelectrophoresis experiment a spherical particle of
3
diameter 0.5 /u.m dispersed in a 0.1 mol. dm," aqueous solution of KCI
at 25°C takes 8.0 s to cover a distance of 120 /n,m along one of the
!
'stationary levels' of the cell, the potential gradient being 10.0 V cm~ .
Calculate

(a) the electrophoretic mobility of the particle;
(b) the probable error in this single mobility determination arising
from the Brownian motion of the particle during the course of
the measurement;
an approximate value for the zeta potential of the particle;
an approximate value for the charge density at the surface of
shear.

31. Spherical particles of radius 0.3 /Ltm suspended in 0.02 mol
dm" 3 KCl(aq.) are observed to have an electrophoretic mobility of
2
1
1
8
4.0 x 10~ m s" V" at 25°C. Calculate an approximate value for
the zeta potential. Briefly mention any simplifications upon which
your calculation is based and in which sense they will affect your
answer.
32. Calculate the rate of electro-osmotic flow of water at 25°C
through a glass capillary tube 10 cm long and 1 mm diameter when
the potential difference between the ends is 200 V. The zeta potential
for the glass-water interface is —40 mV.

7
33. Spherical colloidal particles of diameter 10~ m are dispersed
2 3
in 10~ mol dm" aqueous 1-1 electrolyte at 25°C. The Hamaker