Solute in the context of IUPAC

Potash (/ˈpɒtæʃ/ POT-ash) are mined and manufactured salts that contain potassium in water-soluble form. The term potash derives from pot ash, either plant ashes or wood ashes that were soaked in water in a pot, which was the primary means of manufacturing potash before the Industrial Era; the word potassium derives from the term potash.

In 2021, the worldwide production of potash exceeded 71.9 million tonnes (~45.4 million tonnes K₂O equivalent), and Canada is the greatest producer of potash as fertilizer. Potassium was first derived in 1807 by electrolysis of caustic potash (potassium hydroxide).

In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.

The extent of the solubility of a substance in a specific solvent is generally measured as the concentration of the solute in a saturated solution, one in which no more solute can be dissolved. At this point, the two substances are said to be at the solubility equilibrium. For some solutes and solvents, there may be no such limit, in which case the two substances are said to be "miscible in all proportions" (or just "miscible").

An endorheic lake (also called a sink lake or terminal lake) is a collection of water within an endorheic basin, or sink, with no evident outlet. Endorheic lakes are generally saline as a result of being unable to get rid of solutes left in the lake by evaporation. These lakes can be used as indicators of anthropogenic change, such as irrigation or climate change, in the areas surrounding them. Lakes with subsurface drainage are called cryptorheic.

Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of atmospheric clouds. These aerosols are found in the troposphere, stratosphere, and mesosphere, which collectively make up the greatest part of the homosphere. Clouds consist of microscopic droplets of liquid water (warm clouds), tiny crystals of ice (cold clouds), or both (mixed phase clouds), along with microscopic particles of dust, smoke, or other matter, known as condensation nuclei. Cloud droplets initially form by the condensation of water vapor onto condensation nuclei when the supersaturation of air exceeds a critical value according to Köhler theory. Cloud condensation nuclei are necessary for cloud droplets formation because of the Kelvin effect, which describes the change in saturation vapor pressure due to a curved surface. At small radii, the amount of supersaturation needed for condensation to occur is so large, that it does not happen naturally. Raoult's law describes how the vapor pressure is dependent on the amount of solute in a solution. At high concentrations, when the cloud droplets are small, the supersaturation required is smaller than without the presence of a nucleus.

In warm clouds, larger cloud droplets fall at a higher terminal velocity; because at a given velocity, the drag force per unit of droplet weight on smaller droplets is larger than on large droplets. The large droplets can then collide with small droplets and combine to form even larger drops. When the drops become large enough that their downward velocity (relative to the surrounding air) is greater than the upward velocity (relative to the ground) of the surrounding air, the drops can fall as precipitation. The collision and coalescence is not as important in mixed phase clouds where the Bergeron process dominates. Other important processes that form precipitation are riming, when a supercooled liquid drop collides with a solid snowflake, and aggregation, when two solid snowflakes collide and combine. The precise mechanics of how a cloud forms and grows is not completely understood, but scientists have developed theories explaining the structure of clouds by studying the microphysics of individual droplets. Advances in weather radar and satellite technology have also allowed the precise study of clouds on a large scale.

A solvation shell or solvation sheath is the solvent interface of any chemical compound or biomolecule that constitutes the solute in a solution. When the solvent is water it is called a hydration shell or hydration sphere. The number of solvent molecules surrounding each unit of solute is called the hydration number of the solute.

A classic example is when water molecules arrange around a metal ion. If the metal ion is a cation, the electronegative oxygen atom of the water molecule would be attracted electrostatically to the positive charge on the metal ion. The result is a solvation shell of water molecules that surround the ion. This shell can be several molecules thick, dependent upon the charge of the ion, its distribution and spatial dimensions.

Osmotic concentration, formerly known as osmolarity, 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" (pronounced "molar").

Whereas molarity measures the number of moles of solute per unit volume of solution, osmolarity measures the number of particles on dissociation of osmotically active material (osmoles of solute particles) per unit volume of solution. This value allows the measurement of the osmotic pressure of a solution and the determination of how the solvent will diffuse across a semipermeable membrane (osmosis) separating two solutions of different osmotic concentration.

Molar concentration (also called amount-of-substance concentration or molarity) is the number of moles of solute per liter of solution. Specifically, It is a measure of the concentration of a chemical species, in particular, of a solute in a solution, in terms of amount of substance per unit volume of solution. In chemistry, the most commonly used unit for molarity is the number of moles per liter, having the unit symbol mol/L or mol/dm (1000 mol/m) in SI units. Molar concentration is often depicted with square brackets around the substance of interest; for example, the molarity of the hydronium ion is denoted as [H₃O].

Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential. It is possible to diffuse "uphill" from a region of lower concentration to a region of higher concentration, as in spinodal decomposition. Diffusion is a stochastic process due to the inherent randomness of the diffusing entity and can be used to model many real-life stochastic scenarios. Therefore, diffusion and the corresponding mathematical models are used in several fields beyond physics, such as statistics, probability theory, information theory, neural networks, finance, and marketing.

The concept of diffusion is widely used in many fields, including physics (particle diffusion), chemistry, biology, sociology, economics, statistics, data science, and finance (diffusion of people, ideas, data and price values). The central idea of diffusion, however, is common to all of these: a substance or collection undergoing diffusion spreads out from a point or location at which there is a higher concentration of that substance or collection.

In physical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubility at equilibrium. Most commonly the term is applied to a solution of a solid in a liquid, but it can also be applied to liquids and gases dissolved in a liquid. A supersaturated solution is in a metastable state; it may return to equilibrium by separation of the excess of solute from the solution, by dilution of the solution by adding solvent, or by increasing the solubility of the solute in the solvent.

Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances (principally bacteria), and is used in industrial processes and the production of potable water.

RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. The relative sizes of the various molecules determines what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules (such as solvent molecules, e.g., water).

Osmosis (/ɒzˈmoʊsɪs/, US also /ɒs-/) is the spontaneous net movement of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of higher solute concentration), in the direction that tends to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves across a selectively permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations. Osmosis can be made to do work. Osmotic pressure is defined as the external pressure required to prevent net movement of solvent across the membrane. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity. Osmotic transport occurs through viscous flow of the solvent under a pressure gradient.

Osmosis is a vital process in biological systems, as biological membranes are semipermeable. In general, these membranes are impermeable to large and polar molecules, such as ions, proteins, and polysaccharides, while being permeable to non-polar or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or organelle membranes across the phospholipid bilayer via aquaporins through a selective pore flow mechanism. Osmosis provides the primary means by which water is transported into and out of cells. The turgor pressure of a cell is largely maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment.

Leaching is the process of a solute becoming detached or extracted from its carrier substance by way of a solvent.

Leaching is a naturally occurring process which scientists have adapted for a variety of applications with a variety of methods. Specific extraction methods depend on the soluble characteristics relative to the sorbent material such as concentration, distribution, nature, and size. Leaching can occur naturally seen from plant substances (inorganic and organic), solute leaching in soil, and in the decomposition of organic materials. Leaching can also be applied affectedly to enhance water quality and contaminant removal, as well as for disposal of hazardous waste products such as fly ash, or rare earth elements (REEs). Understanding leaching characteristics is important in preventing or encouraging the leaching process and preparing for it in the case where it is inevitable.

An acidity function is a measure of the acidity of a medium or solvent system, usually expressed in terms of its ability to donate protons to (or accept protons from) a solute (Brønsted acidity). The pH scale is by far the most commonly used acidity function, and is ideal for dilute aqueous solutions. Other acidity functions have been proposed for different environments, most notably the Hammett acidity function, H₀, for superacid media and its modified version H₋ for superbasic media. The term acidity function is also used for measurements made on basic systems, and the term basicity function is uncommon.

Hammett-type acidity functions are defined in terms of a buffered medium containing a weak base B and its conjugate acid BH:

Molecular diffusion is the motion of atoms, molecules, or other particles of a gas or liquid at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid, size and density (or their product, mass) of the particles. This type of diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration.

Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion has ceased and is instead governed by the process of self-diffusion, originating from the random motion of the molecules. The result of diffusion is a gradual mixing of material such that the distribution of molecules is uniform. Since the molecules are still in motion, but an equilibrium has been established, the result of molecular diffusion is called a "dynamic equilibrium". In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing.