Download Chapter 4 1. What is difference between electrophoresis and

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/m3 and
feed concentration 1 kg/m3. 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/m3; C0= 1 kg/m3
cg
(a) J= k ln c 0
= 8.5  10
5
100
ln 1 = 3.7x10-4 m/s
(b) κ2 =(inverse of Debye length)2
=
=
2000 N A Me
2
 k BT
2000 6.02310
808.8510
23
 0.05 (1.610
12
1.3810
23
19 2
)
300
κ-1 =1.38x10-9 m
 E
  e 
 
Q
4 a (1  a )
51.610

43.14808.8510
12
19
710
9
710
(1
1.3810
=
810
6.2210
19
17
(6.07)
=2.1 mv


808.8510
12
e
10
 2.110
3
500
3
=7.43x10-7 m/s
 J 
J
e
 3.7  10
4
 7.43  10
e
-4
3
2
=3.7x10 m /m .s
7
9
9
)