How is an osmole defined?

An osmole is defined as a unit that quantifies the number of particles in a solution. Specifically, it refers to the amount of a substance that, when dissolved, produces one mole of osmotically active particles. This involves considering how many particles a solute dissociates into when it enters solution.

When a substance that has a molecular weight of 1 gram dissociates into multiple ions, the osmole accounts for this dissociation. For example, sodium chloride (NaCl) dissociates into two particles (sodium and chloride ions) when it dissolves; thus, 1 mole of NaCl produces 2 osmoles of particles. This concept is crucial in understanding osmotic pressure and the behavior of solutions in biological and chemical systems.

In contrast, the other definitions do not capture the essence of what an osmole represents. An osmole is specifically related to the dissociation of particles in solution and does not pertain to mass (as in the case of a solvent), volume, or temperature, which are different physical parameters.