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Osmotic pressure is the hydrostatic pressure
Fluid statics

Fluid statics is the science of fluids at rest, and is a sub-field within fluid mechanics. The term usually refers to the mathematical treatment of the subject....
 produced by a difference in concentration between solutions on the two sides of a surface such as a semipermeable membrane. Jacobus Henricus van 't Hoff
Jacobus Henricus van 't Hoff

Jacobus Henricus van 't Hoff was a Netherlands physical chemistry and organic chemistry and the winner of the inaugural Nobel Prize in chemistry....
 first proposed a formula for calculating the osmotic pressure, but this was later improved upon by Harmon Northrop Morse
Harmon Northrop Morse

Harmon Northrop Morse was an American chemist. Today he is known as the first to have synthesized paracetamol, but this substance only became widely used as a drug decades after Morse's death....
.

A related notion, osmotic potential is the opposite of water potential
Water potential

Water potential is the potential energy of water relative to pure free water in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects including surface tension....
, with the former meaning the degree to which a solvent (usually water) would want to stay in a liquid.

i is the dimensionless
Dimensionless quantity

In dimensional analysis, a dimensionless quantity is a quantity without any physical units and thus a pure number. Such a number is typically defined as a product or ratio of quantity which do have units, in such a way that all the units cancel out....
 van 't Hoff factor
Van 't Hoff factor

The van 't Hoff factor is a measure of the effect of a solute upon colligative properties, such as vapor pressure, osmotic pressure and freezing point depression....
M is the molarity
R=0.08206 L · atm · mol-1 · K-1 is the gas constant
Gas constant

The gas constant is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation....
T is the thermodynamic (absolute) temperature
Thermodynamic temperature

Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. Thermodynamic temperature is an ?absolute? scale because it is the measure of the fundamental property underlying temperature: its null or zero point, absolute zero, is the temperature at which the particle constitue...


This equation gives the pressure on one side of the membrane; the total pressure on the membrane is given by the difference between the pressures on the two sides.






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Osmotic pressure is the hydrostatic pressure
Fluid statics

Fluid statics is the science of fluids at rest, and is a sub-field within fluid mechanics. The term usually refers to the mathematical treatment of the subject....
 produced by a difference in concentration between solutions on the two sides of a surface such as a semipermeable membrane. Jacobus Henricus van 't Hoff
Jacobus Henricus van 't Hoff

Jacobus Henricus van 't Hoff was a Netherlands physical chemistry and organic chemistry and the winner of the inaugural Nobel Prize in chemistry....
 first proposed a formula for calculating the osmotic pressure, but this was later improved upon by Harmon Northrop Morse
Harmon Northrop Morse

Harmon Northrop Morse was an American chemist. Today he is known as the first to have synthesized paracetamol, but this substance only became widely used as a drug decades after Morse's death....
.

A related notion, osmotic potential is the opposite of water potential
Water potential

Water potential is the potential energy of water relative to pure free water in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects including surface tension....
, with the former meaning the degree to which a solvent (usually water) would want to stay in a liquid.

Morse equation


The osmotic pressure ? of a dilute solution can be approximated using the Morse equation (named after Harmon Northrop Morse
Harmon Northrop Morse

Harmon Northrop Morse was an American chemist. Today he is known as the first to have synthesized paracetamol, but this substance only became widely used as a drug decades after Morse's death....
):

,

where
i is the dimensionless
Dimensionless quantity

In dimensional analysis, a dimensionless quantity is a quantity without any physical units and thus a pure number. Such a number is typically defined as a product or ratio of quantity which do have units, in such a way that all the units cancel out....
 van 't Hoff factor
Van 't Hoff factor

The van 't Hoff factor is a measure of the effect of a solute upon colligative properties, such as vapor pressure, osmotic pressure and freezing point depression....
M is the molarity
R=0.08206 L · atm · mol-1 · K-1 is the gas constant
Gas constant

The gas constant is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation....
T is the thermodynamic (absolute) temperature
Thermodynamic temperature

Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. Thermodynamic temperature is an ?absolute? scale because it is the measure of the fundamental property underlying temperature: its null or zero point, absolute zero, is the temperature at which the particle constitue...


This equation gives the pressure on one side of the membrane; the total pressure on the membrane is given by the difference between the pressures on the two sides. Note the similarity of the above formula to the ideal gas law
Ideal gas law

The ideal gas law is the equation of state of a hypothetical ideal gas, first stated by Beno?t Paul ?mile Clapeyron in 1834. The law is derived from the fact that in the ideal state of any gas a given number of its "particles" occupy the same volume, and that volume changes are inverse to pressure changes and linear to temperature changes....
 and also that osmotic pressure is not dependent on particle charge. This equation was derived by van 't Hoff
Van 't Hoff

Van 't Hoff may refer to:*Jacobus Henricus van 't Hoff , Dutch chemist...
.

Osmotic pressure is an important factor affecting cells. Osmoregulation
Osmoregulation

Osmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body's water content; that is it keeps the body's fluids from becoming too dilute or too concentrated....
 is the homeostasis
Homeostasis

Homeostasis is the property of a system, either open system or closed system, that regulates its internal environment and tends to maintain a stable, constant condition....
 mechanism of an organism to reach balance in osmotic pressure.

  • Hypertonicity
    Tonicity

    Tonicity measures the ability of a solution to exert an osmotic pressure upon the membrane. Osmolality and osmolarity measure concentration of the solutes independently on their ability to cross the membrane....
     is the presence of a solution that causes cells to shrink. The solution may or may not have a higher osmotic pressure than the cell interior since the rate of water entry will depend upon the permeability of the cell membrane.
  • Hypotonicity
    Tonicity

    Tonicity measures the ability of a solution to exert an osmotic pressure upon the membrane. Osmolality and osmolarity measure concentration of the solutes independently on their ability to cross the membrane....
     is the presence of a solution that causes cells to swell. The solution may or may not have a lower osmotic pressure than the cell interior, since the rate of water entry will depend upon the permeability of the cell membrane.
  • Isotonic
    Tonicity

    Tonicity measures the ability of a solution to exert an osmotic pressure upon the membrane. Osmolality and osmolarity measure concentration of the solutes independently on their ability to cross the membrane....
     is the presence of a solution that produces no change in cell volume.


When a biological
Biological tissue

Tissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function....
 cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 is in a hypotonic environment, the cell interior accumulates water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
, water flows across the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
 into the cell, causing it to expand. In plant cell
Plant cell

Plant cells are eukaryote cells that differ in several key respects from the cell of other eukaryote organisms. Their distinctive features include:...
s, the cell wall
Cell wall

A cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cell . It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism....
 restricts the expansion, resulting in pressure on the cell wall from within called turgor pressure
Turgor pressure

'Turgor pressure' or turgidity is the main pressure of the cell contents against the cell wall in plant cells and bacteria cells, determined by the water content of the vacuole, resulting from osmotic pressure, i.e....
.

Applications

Osmotic pressure is the basis of filtering ("reverse osmosis
Reverse osmosis

Reverse osmosis is a filtration process typically used for water. It works by using pressure to force a solution through a semi-permeable membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side....
"), a process commonly used to purify water. The water to be purified is placed in a chamber and put under an amount of pressure greater than the osmotic pressure exerted by the water and the solutes dissolved in it. Part of the chamber opens to a differentially permeable membrane that lets water molecules through, but not the solute particles. The osmotic pressure of ocean water is about 27 atm
Atmosphere (unit)

The standard atmosphere is an international reference pressure defined as 101,325 Pascal and formerly used as unit of pressure . For practical purposes it has been replaced by the Bar which is 100,000 Pa....
. Reverse osmosis desalinator
Desalination

Desalination, desalinization, or desalinisation refers to any of several processes that remove excess sodium chloride and other minerals from water....
s use pressures around 70 atm to produce fresh water from ocean salt water
Seawater

Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%, or 35 parts per thousand . This means that every 1 kg of seawater has approximately 35 grams of sea salt ....
.

Osmotic pressure is necessary for many plant functions. It is the resulting turgor pressure
Turgor pressure

'Turgor pressure' or turgidity is the main pressure of the cell contents against the cell wall in plant cells and bacteria cells, determined by the water content of the vacuole, resulting from osmotic pressure, i.e....
 on the cell wall that allows herbaceous plants to stand upright, and how plants regulate the aperture of their stomata. In animal cells which lack a cell wall however, excessive osmotic pressure can result in cytolysis
Cytolysis

Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmosis that has caused excess water to move into the cell. It occurs in a Tonicity#Hypotonicity environment, where water Diffusions into the cell and causes its volume to increase....
.
  • Cell wall
    Cell wall

    A cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cell . It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism....
  • Cytolysis
    Cytolysis

    Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmosis that has caused excess water to move into the cell. It occurs in a Tonicity#Hypotonicity environment, where water Diffusions into the cell and causes its volume to increase....
  • Gibbs-Donnan effect
    Gibbs-Donnan effect

    The Gibbs-Donnan effect is a name for the behavior of ions near a semi-permeable membrane to sometimes fail to distribute evenly across the two sides of the membrane....
  • Osmosis
    Osmosis

    Osmosis is the diffusion of a solvent through a Semipermeable membrane, from a solution of low solute concentration to a solution with high solute concentration , up a solute concentration gradient....
  • Pfeffer cell
  • Plasmolysis
    Plasmolysis

    Plasmolysis is the process in plant cells where the plasma membrane pulls away from the cell wall due to the loss of water through osmosis. The reverse process, deplasmolysis, can occur if the cell is in a Tonicity#Hypotonicity solution resulting in a higher external Osmotic_pressure and net flow of water into the cell....
  • Turgor pressure
    Turgor pressure

    'Turgor pressure' or turgidity is the main pressure of the cell contents against the cell wall in plant cells and bacteria cells, determined by the water content of the vacuole, resulting from osmotic pressure, i.e....
For the calculation of molecular weight by using colligative properties, osmotic pressure is the most preferred property.

Potential osmotic pressure

Potential osmotic pressure is the maximum osmotic pressure that could develop in a solution if it were separated from distilled water by a selectively permeable membrane. It is the number of solute particles in a unit volume of the solution that directly determines its potential osmotic pressure. If one waits for equilibrium, osmotic pressure reaches potential osmotic pressure.

See also

  • Jacobus Henricus van 't Hoff
    Jacobus Henricus van 't Hoff

    Jacobus Henricus van 't Hoff was a Netherlands physical chemistry and organic chemistry and the winner of the inaugural Nobel Prize in chemistry....


External links