Chapter 4
1. What is difference between electrophoresis and electroosmosis?
Ans: In electrophoresis, charged solid particles move under external electric field.
In electroosmosis, liquid with free charge move under external electric field
where charged solid is stationary.
2. What is Zeta potential?
Ans: The potential at the stationary outer surface of a charged surface is zeta potential.
3. What is the condition of Debye-Huckel approximation?
Ans: Surface potential is less than 25 mv.
4. What is the scaling length of electric double layer?
Ans: Debye length.
5. A protein solution in 0.05M NaCl is ultrafiltered with mass transfer cooefficient
8x10
-5
m/s. Filtration is gel layer controlled with gel concentration of 100 kg/m
3
and
feed concentration 1 kg/m
3
. Charge on protein is 5e and radius is 7 nm.
(a) What is permeate flux?
(b) If 500 V/m external electric field is applied, what is permeate flux?
Ans: K=8X10
-5
m/s; Cg=100 kg/m
3
; C0= 1 kg/m
3
(a) J=
ln
0
c
g
k
c
=
5
100
8.5 10 ln
1
−
×
= 3.7x10
-4
m/s
(b) κ
2
=(inverse of Debye length)
2
