Question

For each problem determine the osmolarity of each compartment, whether or not osmosis will occur, and if osmosis does occur, in what direction does the water move

6. You have two compartments separated by a membrane which is impermeable to Na₂SO₄. Side A contains distilled water and side B contains 1.0 M Na₂SO₄. What is the osmolarity of the Na₂SO₄ solution? Osmosis will occur. In what direction will the water move? Osmosis will occur until the osmotic pressure of the solution is exactly offset by the hydrostatic pressure of the resulting water column. Assuming complete dissociation of the electrolyte, what is the initial osmotic pressure of the Na₂SO₄ solution?

Answer 1

Na2SO4 ---------> 2Na+ + SO4-2
Concentration of Na2SO4 = 1 M
Osmolarity of Na2SO4 = 3 Osm

Water will move from pure compartment into Na2SO4 solution.
Water potential is defined as the potential energy of water per unit volume. It is denoted by ψ (psi) and is expressed in MPa.
Water potential of pure water is the maximum. It is set at zero. All solutions contain negative water potential. Greater the solution concentration, more negative is the water potential. Water moves from high water potential to lower water potential. Water moves from a hypotonic solution to a hypertonic solution.
Water potential = Pressure potential + Solute potential
Assumption; T = 27'C
Osmotic pressure = iMRT
= 3 X 1 X 0.08206 X 300
= 73.854 atm