Assume that initially the water level in each of the tanks shown below is equal.
ID: 72090 • Letter: A
Question
Assume that initially the water level in each of the tanks shown below is equal. (Also assume that the dimensions of the tanks are equal.) A semi-permeable membrane that permits water movement, but not solute movement, seperates the tanks. The tanks are open to the atmosphere and the temperature is 28oC. When salt ionizes it puts two particles in solution.
Tank A : 0.125 M NaCl
Tank B : Pure Water
(a) At equilibrium which tank will have the highest water level? Explain what causes the change in water level.
(c) What would happen to the flow of water if the pressure in tank A was raised above the value calculated in the preceding question?
(d) Could such a system be used to purify water? How?
Explanation / Answer
(a). Tank A has NaCl that means this tank has hypertonic solution. So, water moves from tank B (pure water) to Tank A to achieve equilibrium due to osmosis. Therefore, Tank A will have the highest water level after achieving equilibrium.
(c) If the pressure in tank A was raised, then the water flows in reverse to the tank B even though the solution in tank B is hypotonic to the tank A.
(d) Yes, this system applies the phenomenon called reverse osmosis. In reverse osmosis, an applied pressure is used to overcome osmotic pressure. This process produces pure water.