Question

8. (5 pts.) An engineer is using reverse osmosis ("RO") to desalinate a tank of contaminated water that has a concentration of 0.128 M CaCl, at 35.00°C to form deionized water (1 x 108 M). Given that 1 atm = 14.7 psi, the pressure he/she needed to apply across the “RO” membrane should be: (a) 143 psi (b) 92.6 psi (c) 15.6 psi (d) 185 psi

Answer 1

Q8. Given : concentration of CaCl2 = 0.128 M

Osmotic pressure = i * C * R * T

where i = van't Hoff factor = number of particles or ions obtained after dissociation = 3 (for CaCl2)

C = concentration of CaCl2 = 0.128 M

R = constant = 0.0821 atm/M-K

T = absolute temperature = 35oC = (35 + 273) K = 308 K

Substituting the values,

Osmotic pressure = (3) * (0.128 M) * (0.0821 atm/M-K) * (308 K)

Osmotic pressure = 9.71 atm

Osmotic pressure = 9.71 atm * (14.7 psi)

Osmotic pressure = 143 psi

Correct option is : (a) 143 psi