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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 6.02310 808.8510 23 0.05 (1.610 12 1.3810 23 19 2 ) 300 κ-1 =1.38x10-9 m E e Q 4 a (1 a ) 51.610 43.14808.8510 12 19 710 9 710 (1 1.3810 = 810 6.2210 19 17 (6.07) =2.1 mv 808.8510 12 e 10 2.110 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 )