Question

A reverse osmosis unit is used to obtain drinkable water from a source that contains 0.530 g NaCl per liter. What is the minimum pressure (in torr) that must be applied across the semipermeable membrane to obtain water? Assume room temperature or about 298 K. (Don′t forget the van′t Hoff factor!)

I'm not really sure what to do with this question. I know for osmotic pressure, the equation is iMRT, but I don't know what exactly to do.

Answer 1

This should get you started.
You know M NaCl = grams/molar mass and that's in 1 L so that is the molarity.
i = van't Hoff factor = 2 for NaCl
R is 0.08206
T = 298.
solve for pi (in atm) and convert to torr..