What are the differences between molarity and osmolarity?

Question

Accepted Answer

Basis of differentiation

Molarity

Osmolarity

Definition

The concentration of a solute in a solution, expressed as the number of moles of solute per liter of solution

The concentration of all osmotically active particles in a solution, expressed as the number of osmoles (or milliosmoles) of solute per liter of solution

Units

mol/L (molar)

osmol/L (osmolar) or mOsmol/L (milliosmolar)

Dilution factor

Molarity changes upon dilution but the total number of moles of solute remains constant

Diluting a solution involves adding more solvent, which increases the total volume and decreases the concentration, while the amount of solute remains constant

Components

Involves only the number of moles of solute present

Involves all particles that contribute to osmotic pressure, including ions and molecules

Basis of differentiation	Molarity	Osmolarity
Definition	The concentration of a solute in a solution, expressed as the number of moles of solute per liter of solution	The concentration of all osmotically active particles in a solution, expressed as the number of osmoles (or milliosmoles) of solute per liter of solution
Units	mol/L (molar)	osmol/L (osmolar) or mOsmol/L (milliosmolar)
Dilution factor	Molarity changes upon dilution but the total number of moles of solute remains constant	Diluting a solution involves adding more solvent, which increases the total volume and decreases the concentration, while the amount of solute remains constant
Components	Involves only the number of moles of solute present	Involves all particles that contribute to osmotic pressure, including ions and molecules

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