How can molarity and osmolarity be calculated from mass per unit volume?
Assume you have a solution that contains 40.0 g of NaCl in 1.00 L of solution.
The molarity of a solution is the number of moles of solute per litre of solution.
You have to convert the mass of NaCl to moles of NaCl.
Moles of NaCl = 40.0 g NaCl ×
An ionic compound such as NaCl separates into cations and anions on dissolving.
NaCl(s) →Na⁺(aq) + Cl⁻(aq)
Osmosis depends on the number of solute particles in a solution. Both the number of moles of Na+ and the number of moles of Cl- contribute to the osmotic pressure. Thus, 1 mol of NaCl gives 2 mol of osmotic particles.
Each mole of solute that contributes to the osmotic pressure of a solution is an osmole.
The osmolarity is the molarity of the compound times the number of particles produced by one mole of compound.
The osmolarity of the NaCl solution is