What is osmotic pressure?
Osmosis refers to the one-way spontaneous diffusion of solvent molecules through a semi-impermeable membrane from the least concentrated to the more concentrated solution. A semi-impermeable membrane is one that is permeable to solvent cells and impermeable to particles dissolved in it. By definition, osmotic pressure is such a hydrostatic pressure, the application of which to this solution can stop the diffusion of particles, that is, osmosis.
Osmosis is widespread in nature. It is characteristic of all biological organisms. Osmotic pressure occurs if the solutions are separated by a semipermeable membrane. For example, take fluids in cells and in the intercellular space. Normally, extracellular and intracellular osmotic pressure are the same. But if the interstitial fluid loses water, the pressure in it increases. Under the influence of increased osmotic pressure, water from the cells begins to diffuse into the intercellular space. Diffusion will stop only when the pressure values equalize.
What does osmotic pressure depend on?
Osmosis pressure depends on how many dissolved particles are contained in a unit volume. It can be molecules, ions or other colloidal particles. We can say that the osmotic pressure of the solution is associated with the concentration of all particles active osmotically in a unit volume. It does not depend on the chemical properties of the solvent and the substances dissolved in it.
Scientists have found that osmotic pressure obeys the same laws as gas pressure. It can be measured using instruments called osmometers. They are a special kind of pressure gauges. These devices use semi-impermeable membranes of animal and artificial origin. Pressure measurements show its direct dependence on the concentration of the solution.
The law of osmotic pressure, discovered by Van Hoff, states that its value in numerical terms is equal to the pressure that the substance of a given solution would exert, being at that temperature an ideal gas, provided that its volume would be equal to the volume of the solution.
The law is described by the equation: p = i CRT
i– isotonic coefficient value;
C is the concentration of the solution, expressed in moles;
R is the value of the universal gas constant;
T is the thermodynamic temperature.
The importance of osmotic pressure for living organisms
Osmosis is inherent in wildlife, since all cells of plants and animal organisms have membranes that are permeable to water and impermeable to other substances. In living tissues, at the border of the cell and intercellular fluid, osmotic pressure is constantly acting. It provides the rise of nutrients and water from the earth to the leaves of plants and turgor of plants, the vital activity of cells.
Solutions with the same osmotic pressure are called isotonic. Those in which the pressure is higher are called hypertonic, lower - hypotonic.
The osmotic pressure in human blood is 7.7 atm. People are able to feel the slightest of his fluctuations. For example, thirst after eating salty foods is associated with its increase. Local edema with inflammation also occurs due to an increase in osmotic pressure at the site of inflammation.
Knowledge of the laws of osmotic pressure in medicine is necessary when conducting therapeutic measures. So, doctors know that for intravenous administration, only 0.9% NaCl solution can be used in isotonic plasma. It does not cause tissue irritation. On the contrary, hypertonic 3-5% NaCl is used to better cleanse purulent wounds from microorganisms and pus.
Knowledge of the laws of osmosis is necessary not only in medicine and biology. Many types of human activity, including industry and energy, cannot do without it.