A. The wastewater solution from a factory containing high levels of salts needs

Question

A. The wastewater solution from a factory containing high levels of salts needs to be diluted before it can be released into the environment. Therefore, two containers of waste solution are separated by a semipermeable membrane and pressure is applied to one container, forcing only water molecules through the membrane and diluting the waste solution in the other container. As dilution continues, higher and higher pressures are needed to counteract the natural tendency for the water molecules to have a net flow back toward the more concentrated solution.
What was the applied pressure at the end of this process if the final concentrations of the solutions were 0.052M and 0.190M at a temperature of 23 ?C?

B. There are limitations to the amount of pressure that can be applied during reverse osmosis because of the physical nature of the membrane. A membrane has been developed that can withstand osmotic pressures, ?, of up to 1.51

Explanation / Answer

Part A :

At the end, difference in concentrations of two solutions, C" = 0.190-0.052 = 0.138 mol L-1 = 138 mol m-3

Temperature, T = 23'C = 296 K
Thus, applied pressure at end of process , P = C"*R*T = 138*8.314*296 = 339.610 kJ/m3 = 339.61kPa

Part B :

Maximum pressure, P = 1.51*105 torr = 201.31*105 Pa

T = 25'C = 298 K

Thus, C" = P/(RT) = (201.31*105)/(8.314*298) = 8125.29 mol m-3 = 8.125 mol L-1 = 8.125 M

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