Difference between osmolarity and tonicity
Key difference
Comparative chart
| Osmolarity | Tonicity | |
| Definition | Osmolarity is the concentration of a solution expressed as the total number of solute particles per liter. | Tonicity is the measure of the effective atmospheric gradient and the ability of the extracellular solution to cause the solution to enter or leave a cell with the process of osmosis. |
| Concentration | Osmolarity takes into account all solute concentrations. | Tonicity only considers solutes that failed to cross the semipermeable membrane. |
| Measurement units | osmol / L | prostitute |
What is osmolarity?
Osmolarity is the concentration of a solution expressed as the total number of solute particles per liter. Consider all the solutes in the solution, whether they are permeable or non-permeable. It is the measure of the solute concentration per unit volume, and is denoted using osmoles present in the solution. In most cases, the osmolarity value is similar to the molarity value. They are quite different though, as osmolarity implies the total amount of solutes in a solution, while molarity is roughly the total concentration of the compound. Osmolarity can be further divided into three ways relative to the osmotic pressure of the solution. 1) Isosmotic solution: The atmospheric pressure of the solution is equal to that of the environment. 2) Hyperosmotic solution: The atmospheric pressure of the solution is higher than that of the surroundings. 3) Hypoosmotic solution: The atmospheric pressure of the solution is lower than that of the environment.
What is tonicity?
Tonicity is the measure of the effective atmospheric gradient and the ability of the extracellular solution to cause the solution to enter or leave a cell with the process of osmosis. Unlike osmolarity, tonicity only considers the solutes that failed to cross the semipermeable membrane, since they are the only solutes that influence the osmotic pressure gradient. Solutes that freely cross the membrane do not affect tonicity because they always remain in equal concentrations on both sides of the membranes. Tonicity is often misunderstood when it is called the measure of osmotic pressure itself. It is actually the measure of the osmotic pressure gradient. Generally used when describing the response of cells immersed in an external solution.
Osmolarity vs. tonicity
- Osmolarity is the concentration of a solution expressed as the total number of solute particles per liter, while tonicity is the measure of the effective atmospheric gradient and the ability of the extracellular solution to cause the solution to enter or leave a cell with the osmosis process.
- Osmolarity takes all solute concentrations under consideration, while tonicity only considers solutes that did not pass through the semipermeable membrane.
- Osmolarity is expressed as osmol / L, while tonicity is denoted using mol / L.
