In reverse osmosis, water flows out of a salt solution until the osmotic pressure of the solution equals the applied pressure. If a pressure of 42.0 bar is applied to seawater, what will be the final concentration of the seawater at 20 °C when reverse osmosis stops?
Assuming that seawater has a total ion concentration (a.k.a colligative molarity) of 1.10 Mc, calculate how many liters of seawater are needed to produce 50.2 L of fresh water at 20 °C with an applied pressure of 42.0 bar.

Question

In reverse osmosis, water flows out of a salt solution until the osmotic pressure of the solution equals the applied pressure. If a pressure of 42.0 bar is applied to seawater, what will be the final concentration of the seawater at 20 °C when reverse osmosis stops?
Assuming that seawater has a total ion concentration (a.k.a colligative molarity) of 1.10 Mc, calculate how many liters of seawater are needed to produce 50.2 L of fresh water at 20 °C with an applied pressure of 42.0 bar.

anonymous · Answer

i would go about this by asking: how is the osmotic pressure related to the concentration "gradient" across the membrane? this is the pressure needed to keep the water from pushing its way back from the side with the lower solute concentration. 

when there is no net movement of water across the membrane, how is the pressure we are applying related to the pressure of the water trying to push back?