Anelectrolyte is a substance that conductselectricity through the movement ofions, but not through the movement ofelectrons.^[1][2][3] This includes most solublesalts,acids, andbases, dissolved in apolar solvent like water. Upon dissolving, the substance separates intocations andanions, which disperse uniformly throughout the solvent.^[4]Solid-state electrolytes also exist. In medicine and sometimes in chemistry, the term electrolyte refers to the substance that is dissolved.^[5][6]

Electrically, such a solution is neutral. If anelectric potential is applied to such a solution, the cations of the solution are drawn to theelectrode that has an abundance ofelectrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current. Some gases, such ashydrogen chloride (HCl), under conditions of high temperature or low pressure can also function as electrolytes.^{[clarification needed]} Electrolyte solutions can also result from the dissolution of some biological (e.g.,DNA,polypeptides) orsynthetic polymers (e.g.,polystyrene sulfonate), termed "polyelectrolytes", which contain chargedfunctional groups. A substance that dissociates into ions in solution or in the melt acquires the capacity to conduct electricity.Sodium,potassium,chloride,calcium,magnesium, andphosphate in a liquid phase are examples of electrolytes.

In medicine,electrolyte replacement is needed when a person has prolongedvomiting ordiarrhea, and as a response to sweating due to strenuous athletic activity. Commercial electrolyte solutions are available, particularly for sick children (such asoral rehydration solution,Suero Oral, orPedialyte) and athletes (sports drinks). Electrolyte monitoring is important in the treatment ofanorexia andbulimia.

In science, electrolytes are one of the main components ofelectrochemical cells.^[2]

In clinicalmedicine, mentions of electrolytes usually refermetonymically to the ions, and (especially) to theirconcentrations (in blood, serum, urine, or other fluids). Thus, mentions of electrolyte levels usually refer to the various ion concentrations, not to the fluid volumes.

The wordelectrolyte derives fromAncient Greek ήλεκτρο- (ēlectro-), prefix originally meaningamber but in modern contexts related to electricity, and λυτός (lytos), meaning "able to be taken apart".^[7]

In his 1884 dissertation,Svante Arrhenius put forth his explanation of solid crystalline salts disassociating into paired charged particles when dissolved, for which he won the 1903Nobel Prize in Chemistry.^{[8][9][10][11]} Arrhenius's explanation was that in forming a solution, the salt dissociates into charged particles, to whichMichael Faraday (1791-1867) had given the name "ions" many years earlier. Faraday's belief had been that ions were produced in the process ofelectrolysis. Arrhenius proposed that, even in the absence of an electric current, solutions of salts contained ions. He thus proposed that chemical reactions in solution were reactions between ions.^[9][10][11]

Shortly after Arrhenius's hypothesis of ions,Franz Hofmeister and Siegmund Lewith^[12][13][14] found that different ion types displayed different effects on such things as the solubility of proteins. A consistent ordering of these different ions on the magnitude of their effect arises consistently in many other systems as well. This has since become known as theHofmeister series.

While the origins of these effects are not abundantly clear and have been debated throughout the past century, it has been suggested that the charge density of these ions is important^[15] and might actually have explanations originating from the work ofCharles-Augustin de Coulomb over 200 years ago.

Electrolyte solutions are normally formed when salt is placed into asolvent such as water and the individual components dissociate due to thethermodynamic interactions between solvent and solute molecules, in a process called "solvation". For example, when table salt (sodium chloride), NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction:^{[citation needed]}

NaCl_(s) → Na⁺_(aq) + Cl⁻_(aq)

It is also possible for substances to react with water, producing ions. For example,carbon dioxide gas dissolves in water to produce a solution that containshydronium,carbonate, andhydrogen carbonate ions.^{[citation needed]}

Molten salts can also be electrolytes as, for example, when sodium chloride is molten, the liquid conducts electricity. In particular, ionic liquids, which are molten salts with melting points below 100 °C,^[16] are a type of highly conductive non-aqueous electrolytes and thus have found more and more applications in fuel cells and batteries.^[17]

An electrolyte in a solution may be described as "concentrated" if it has a high concentration of ions, or "dilute" if it has a low concentration. If a high proportion of the solute dissociates to form free ions, the electrolyte is strong; if most of the solute does not dissociate, the electrolyte is weak. The properties of electrolytes may be exploited using electrolysis to extract constituent elements and compounds contained within the solution.^{[citation needed]}

Alkaline earth metals form hydroxides that are strong electrolytes with limited solubility in water, due to the strong attraction between their constituent ions. This limits their application to situations where high solubility is required.^[18]

In 2021, researchers have found that electrolyte can "substantially facilitate electrochemical corrosion studies in less conductive media".^[19]

Inphysiology, the primary ions of electrolytes aresodium (Na⁺),potassium (K⁺),calcium (Ca²⁺),magnesium (Mg²⁺),chloride (Cl⁻),hydrogen phosphate (HPO₄²⁻), andhydrogen carbonate (HCO₃⁻).^{[20][failed verification]} The electric charge symbols of plus (+) and minus (−) indicate that the substance is ionic in nature and has an imbalanced distribution of electrons, the result ofchemical dissociation. Sodium is the main electrolyte found in extracellular fluid and potassium is the main intracellular electrolyte;^[21] both are involved in fluid balance andblood pressure control.^[22]

All known multicellular lifeforms require a subtle and complex electrolyte balance between theintracellular andextracellular environments.^[20] In particular, the maintenance of preciseosmoticgradients of electrolytes is important. Such gradients affect and regulate thehydration of the body as well asblood pH, and are critical fornerve andmuscle function. Various mechanisms exist in living species that keep the concentrations of different electrolytes under tight control.^[23]

Both muscle tissue andneurons are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between theextracellular fluid orinterstitial fluid, andintracellular fluid. Electrolytes may enter or leave the cell membrane through specialized protein structures embedded in theplasma membrane called "ion channels". For example,muscle contraction is dependent upon the presence of calcium (Ca²⁺), sodium (Na⁺), and potassium (K⁺). Without sufficient levels of these key electrolytes, muscle weakness or severe muscle contractions may occur.^{[citation needed][24]}

Electrolyte balance is maintained by oral, or in emergencies, intravenous (IV) intake of electrolyte-containing substances, and is regulated byhormones, in general with thekidneys flushing out excess levels. In humans, electrolytehomeostasis is regulated by hormones such asantidiuretic hormones,aldosterone andparathyroid hormones. Seriouselectrolyte disturbances, such asdehydration andoverhydration, may lead to cardiac and neurological complications and, unless they are rapidly resolved, will result in amedical emergency.

Measurement of electrolytes is a commonly performed diagnostic procedure, performed viablood testing withion-selective electrodes orurinalysis bymedical technologists. The interpretation of these values is somewhat meaningless without analysis of theclinical history and is often impossible without parallel measurements ofrenal function. The electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except forarterial blood gas interpretations since they are inherently linked to sodium levels. One important test conducted on urine is thespecific gravity test to determine the occurrence of anelectrolyte imbalance.^{[citation needed]}

According to a study paid for by theGatorade Sports Science Institute, electrolyte drinks containing sodium and potassium salts replenish the body's water and electrolyte concentrations after dehydration caused byexercise,excessive alcohol consumption,diaphoresis (heavy sweating), diarrhea, vomiting,intoxication or starvation; the study says that athletes exercising in extreme conditions (for three or more hours continuously, e.g. amarathon ortriathlon) who do not consume electrolytes riskdehydration (orhyponatremia).^{[25][needs independent confirmation]}

A home-made electrolyte drink can be made by using water, sugar and saltin precise proportions.^[26] It is important to includeglucose (sugar) to utilise the co-transport mechanism of sodium and glucose. Commercial preparations are also available^[27] for both human and veterinary use.

Electrolytes are commonly found infruit juices, sports drinks, milk, nuts, and many fruits and vegetables (whole or in juice form) (e.g., potatoes,avocados).

Whenelectrodes are placed in an electrolyte and avoltage is applied, the electrolyte will conduct electricity. Loneelectrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at thecathode, providing electrons to the electrolyte. Another reaction occurs at theanode, consuming electrons from the electrolyte. As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode. The ions in the electrolyte neutralize these charges, enabling the electrons to keep flowing and the reactions to continue.^{[citation needed]}

For example, in a solution of ordinary table salt (sodium chloride, NaCl) in water, the cathode reaction will be

2 H₂O + 2e⁻ → 2 OH⁻ + H₂

andhydrogen gas will bubble up; the anode reaction is

2 NaCl → 2 Na⁺ + Cl₂ + 2e⁻

andchlorine gas will be liberated into solution where it reacts with the sodium and hydroxyl ions to producesodium hypochlorite - householdbleach. The positively charged sodium ions Na⁺ will react toward the cathode, neutralizing the negative charge of OH⁻ there, and the negatively charged hydroxide ions OH⁻ will react toward the anode, neutralizing the positive charge of Na⁺ there. Without the ions from the electrolyte, the charges around the electrode would slow down continued electron flow;diffusion of H⁺ and OH⁻ through water to the other electrode takes longer than movement of the much more prevalent salt ions.Electrolytes dissociate in water because water molecules are dipoles and the dipoles orient in an energetically favorable manner tosolvate the ions.

In other systems, the electrode reactions can involve the metals of the electrodes as well as the ions of the electrolyte.

Electrolytic conductors are used in electronic devices where the chemical reaction at a metal-electrolyte interface yields useful effects.

• Inbatteries, two materials with different electron affinities are used as electrodes; electrons flow from one electrode to the other outside of the battery, while inside the battery the circuit is closed by the electrolyte's ions. Here, the electrode reactions convert chemical energy to electrical energy.^[28]
• In somefuel cells, a solid electrolyte orproton conductor connects the plates electrically while keeping the hydrogen and oxygen fuel gases separated.^[29]
• Inelectroplating tanks, the electrolyte simultaneously deposits metal onto the object to be plated, and electrically connects that object in the circuit.
• In operation-hours gauges, two thin columns ofmercury are separated by a small electrolyte-filled gap, and, as charge is passed through the device, the metal dissolves on one side and plates out on the other, causing the visible gap to slowly move along.
• Inelectrolytic capacitors the chemical effect is used to produce an extremely thindielectric orinsulating coating, while the electrolyte layer behaves as one capacitor plate.
• In somehygrometers the humidity of air is sensed by measuring the conductivity of a nearly dry electrolyte.
• Hot, softened glass is an electrolytic conductor, and some glass manufacturers keep the glass molten by passing a large current through it.

Solid electrolytes can be mostly divided into four groups described below.

Gel electrolytes – closely resemble liquid electrolytes. In essence, they are liquids in a flexiblelattice framework. Variousadditives are often applied to increase theconductivity of such systems.^[28][30]

Solid ceramic electrolytes –ions migrate through the ceramic phase by means of vacancies orinterstitials within thelattice. There are alsoglassy-ceramic electrolytes.

Dry polymer electrolytes differ from liquid and gel electrolytes in that salt is dissolved directly into the solid medium. Usually it is a relatively high-dielectric constantpolymer (PEO,PMMA,PAN,polyphosphazenes,siloxanes, etc.) and a salt with lowlattice energy. In order to increase themechanical strength and conductivity of such electrolytes, very oftencomposites are made, and inert ceramic phase is introduced. There are two major classes of such electrolytes: polymer-in-ceramic, and ceramic-in-polymer.^[31][32][33]

Organic ionic plastic crystals – are a typeorganic salts exhibitingmesophases (i.e. astate of matter intermediate between liquid and solid), in which mobile ions are orientationally or rotationally disordered while their centers are located at the ordered sites in the crystal structure.^[29] They have various forms of disorder due to one or more solid–solidphase transitions below themelting point and have thereforeplastic properties and good mechanical flexibility as well as an improved electrode-electrolyte interfacial contact. In particular, protic organic ionic plastic crystals (POIPCs),^[29] which are solidprotic organic salts formed byproton transfer from aBrønsted acid to a Brønsted base and in essence are proticionic liquids in themolten state, have found to be promising solid-stateproton conductors forfuel cells. Examples include1,2,4-triazoliumperfluorobutanesulfonate^[29] andimidazoliummethanesulfonate.^[34]

• Electrochemical machining
• Elektrolytdatenbank Regensburg
• Ion transport number
• ITIES (interface between two immiscible electrolyte solutions)
• Salt bridge
• Strong electrolyte
• Supporting electrolyte (background electrolyte)
• VTPR

•   Media related toElectrolytes at Wikimedia Commons
• Friedman HL (1960)."Mayer's Ionic Solution Theory Applied to Electrolyte Mixtures".The Journal of Chemical Physics.32 (4):1134–1149.Bibcode:1960JChPh..32.1134F.doi:10.1063/1.1730863.
• Leaist DG, Lyons PA (1981). "Multicomponent diffusion of electrolytes with incomplete dissociation. Diffusion in a buffer solution".The Journal of Physical Chemistry.85 (12):1756–1762.doi:10.1021/j150612a033.
• Kaminsky M (1957). "Ion-solvent interaction and the viscosity of strong-electrolyte solutions".Discussions of the Faraday Society.24: 171.doi:10.1039/DF9572400171.