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Osmotic concentration, formerly known as osmolarity, [1] is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L (pronounced "osmolar"), in the same way that the molarity of a solution is expressed as "M ...
The laboratory value measures the freezing point depression, properly called osmolality while the calculated value is given in units of osmolarity. Even though these values are presented in different units, when there is a small amount of solute compared to total volume of solution, the absolute values of osmolality vs. osmolarity are very close.
For most non-electrolytes dissolved in water, the van 't Hoff factor is essentially 1. For most ionic compounds dissolved in water, the van 't Hoff factor is equal to the number of discrete ions in a formula unit of the substance. This is true for ideal solutions only, as occasionally ion pairing occurs in solution. At a given instant a small ...
where is the chemical potential of the pure solvent and is the chemical potential of the solvent in a solution, M A is its molar mass, x A its mole fraction, R the gas constant and T the temperature in Kelvin. [1] The latter osmotic coefficient is sometimes called the rational osmotic coefficient. The values for the two definitions are ...
When a measure of serum solutes is calculated, it is often done in units of osmolarity. While it is possible to convert between osmolality and osmolarity, [6] thereby deriving a more mathematically correct osmol gap calculation, in actual clinical practice this is not done. This is because the difference in absolute value of these two ...
The osmometer uses the solution's freezing point depression to establish its strength. It is also used to determine the level of osmotically appropriate body fluid in various chemicals dissolved in the blood using the relationship in which a mole of dissolved substance reduces the freezing point of a kilogram of water by 1.86 °C (35.35 °F). [1]
1. To calculate an estimation, the total amount of substance in the body before the loss is first estimated: = where: n b = Total amount of substance before fluid loss; Osm b = Body osmolarity before loss (almost equal to plasma osmolality of 275-299 milli-osmoles per kilogram [4])
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. [1] It is also defined as the measure of the tendency of a solution to take in its pure solvent by osmosis .