Instructions
Osmolarity of a Mixture
Measure the amounts of each component substance within the mixture.
Determine the number of osmoles per unit of measure, which are particles that will not disassociate when disolved.
Multiply the osmoles per unit/measure for each substance by the volume of that substance. For example, if a solution is made up of three substances, one with a volume of 50 liters and an osmoles per unit/measure of 2 osmoles per liter, one with 10 L and 4 Osm/L and one with 5 L and 2 Osm/L, multiply the volume of each substance by its Osm/L. So, (50 L * 2 Osm/L) = 100 Osmoles, (10 L * 4 Osm/L) = 40 Osmoles and (5 L * 2 Osm/L) = 10 Osmoles.
Add the values of osmoles together to determine the osmolarity of the whole mixture. For example, if three component substances of a mixture contain 100 Osmoles, 40 Osmoles and 10 Osmoles, the entire mixture contains (100 Osm + 40 Osm + 10 Osm) = 150 Osm.
Osmolarity from Molarity
Add up the total number of atoms per molecule of substance. For example, MgCl2 has three atoms, 1 Mg atom and 2 Cl atoms.
Measure the molarity of the solution. Molarity equals the number of moles of a solute (the substance being dissolved) divided by the number of liters of the entire solution.
Multiply the molarity of the solution by the number of atoms per molecule. For example, a solution of MgCl2, NaCl and glucose with a molarity of 3 M and (1 Mg + 3 Cl + 1 Na + 1 glucose) = 6 atoms, becomes: (3 M * 6 atoms) = 18 Osm.