An electrolyte is a medium containing
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s that is
electrically conducting through the movement of those ions, but not conducting
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
s.
This includes most soluble
salts
In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...
,
acids, and
bases dissolved in a
polar solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...
, such as water. Upon dissolving, the substance separates into
cations and
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s, which disperse uniformly throughout the solvent.
Solid-state electrolyte
A solid-state electrolyte (SSE) is a solid ionic conductor and electron-insulating material and it is the characteristic component of the solid-state battery. It is useful for applications in electrical energy storage (EES) in substitution of the ...
s also exist. In medicine and sometimes in chemistry, the term electrolyte refers to the substance that is dissolved.
Electrically, such a solution is neutral. If an
electric potential
The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...
is applied to such a solution, the cations of the solution are drawn to the
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...
that has an abundance of
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
s, 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 as
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
(HCl), under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological (e.g.,
DNA,
polypeptides
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
A p ...
) or
synthetic polymers (e.g.,
polystyrene sulfonate
Polystyrene sulfonates are a group of medications used to treat high blood potassium. Effects generally take hours to days. They are also used to remove potassium, calcium, and sodium from solutions in technical applications.
Common side effect ...
), termed "
polyelectrolyte
Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Polycations and polyanions are polyelectrolytes. These groups dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are ...
s", which contain charged
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
s. A substance that dissociates into ions in solution or in the melt acquires the capacity to conduct electricity.
Sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
,
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
,
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride sa ...
,
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, and
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
in a liquid phase are examples of electrolytes.
In medicine,
electrolyte replacement is needed when a person has prolonged
vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose.
Vomiting can be the result of ailments like food poisoning, gastroenteri ...
or
diarrhea
Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
, and as a response to sweating due to strenuous athletic activity. Commercial electrolyte solutions are available, particularly for sick children (such as
oral rehydration solution,
Suero Oral, or
Pedialyte
Pedialyte is an oral electrolyte solution manufactured by Abbott Laboratories and marketed for use in children. It was invented by Dr. Gary Cohen of Swampscott, Massachusetts.
Description
Pedialyte is designed to promote rehydration and elect ...
) and athletes (
sports drink
Sports drinks, also known as electrolyte drinks, are functional beverages whose stated purpose is to help athletes replace water, electrolytes, and energy before, during and especially after training or competition. There are many perceived bene ...
s). Electrolyte monitoring is important in the treatment of
anorexia
Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...
and
bulimia
Bulimia nervosa, also known as simply bulimia, is an eating disorder characterized by binge eating followed by purging or fasting, and excessive concern with body shape and weight. The aim of this activity is to expel the body of calories eaten ...
.
In science, electrolytes are one of the main components of
electrochemical cell
An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic o ...
s.
Etymology
The word ''electrolyte'' derives from
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
ήλεκτρο- (''ēlectro''-), prefix related to electricity, and λυτός (''lytos''), meaning "able to be untied or loosened".
History
![Arrhenius2](https://upload.wikimedia.org/wikipedia/commons/6/6c/Arrhenius2.jpg)
In his 1884 dissertation,
Svante Arrhenius
Svante August Arrhenius ( , ; 19 February 1859 – 2 October 1927) was a Swedish scientist. Originally a physicist, but often referred to as a chemist, Arrhenius was one of the founders of the science of physical chemistry. He received the Nob ...
put forth his explanation of solid crystalline salts disassociating into paired charged particles when dissolved, for which he won the 1903 Nobel Prize in Chemistry.
Arrhenius's explanation was that in forming a solution, the salt dissociates into charged particles, to which
Michael Faraday
Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
(1791-1867) had given the name "
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s" many years earlier. Faraday's belief had been that ions were produced in the process of
electrolysis. 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.
Shortly after Arrhenius's hypothesis of ions,
Franz Hofmeister
Franz Hofmeister (30 August 1850, in Prague – 26 July 1922, in Würzburg) was an early protein scientist, and is famous for his studies of salts that influence the solubility and conformational stability of proteins. In 1902, Hofmeister became t ...
and Siegmund Lewith 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 the
Hofmeister 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 and might actually have explanations originating from the work of
Charles-Augustin de Coulomb
Charles-Augustin de Coulomb (; ; 14 June 1736 – 23 August 1806) was a French officer, engineer, and physicist. He is best known as the eponymous discoverer of what is now called Coulomb's law, the description of the electrostatic force of attra ...
over 200 years ago.
Formation
Electrolyte solutions are normally formed when salt is placed into a
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
such as water and the individual components dissociate due to the
thermodynamic
Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...
interactions between solvent and solute molecules, in a process called "
solvation
Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the ...
". 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
:NaCl
(s) → Na
+(aq) + Cl
−(aq)
It is also possible for substances to react with water, producing ions. For example,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
gas dissolves in water to produce a solution that contains
hydronium
In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid i ...
,
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
, and
hydrogen carbonate ions.
Molten salt
Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.Journal of Chemical T ...
s 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, are a type of highly conductive non-aqueous electrolytes and thus have found more and more applications in fuel cells and batteries.
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.
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.
In 2021 researchers have found that electrolyte can "substantially facilitate electrochemical corrosion studies in less conductive media".
Physiological importance
In
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
, the primary ions of electrolytes are
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
(Na
+),
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
(K
+),
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
(Ca
2+),
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
(Mg
2+),
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride sa ...
(Cl
−),
hydrogen phosphate (HPO
42−), and
hydrogen carbonate (HCO
3−).
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 of
chemical dissociation. Sodium is the main electrolyte found in extracellular fluid and potassium is the main intracellular electrolyte; both are involved in fluid balance and
blood pressure control.
All known multicellular lifeforms require a subtle and complex electrolyte balance between the
intracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
and
extracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
environments.
In particular, the maintenance of precise
osmotic
Osmosis (, ) is the spontaneous net movement or diffusion 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 o ...
gradient
In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gr ...
s of electrolytes is important. Such gradients affect and regulate the
hydration Hydration may refer to:
* Hydrate, a substance that contains water
* Hydration enthalpy, energy released through hydrating a substance
* Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound
* ...
of the body as well as
blood pH
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the ...
, and are critical for
nerve and
muscle function. Various mechanisms exist in living species that keep the concentrations of different electrolytes under tight control.
Both muscle tissue and
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between the
extracellular fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a low ...
or
interstitial fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower ...
, and
intracellular fluid
The human body and even its individual body fluids may be conceptually divided into various fluid compartments, which, although not literally anatomic compartments, do represent a real division in terms of how portions of the body's water, solute ...
. Electrolytes may enter or leave the cell membrane through specialized protein structures embedded in the
plasma membrane called "
ion channels". For example,
muscle contraction
Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as ...
is dependent upon the presence of calcium (Ca
2+), sodium (Na
+), and potassium (K
+). Without sufficient levels of these key electrolytes, muscle weakness or severe muscle contractions may occur.
Electrolyte balance is maintained by oral, or in emergencies, intravenous (IV) intake of electrolyte-containing substances, and is regulated by
hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
s, in general with the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
s flushing out excess levels. In humans, electrolyte
homeostasis
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
is regulated by hormones such as
antidiuretic hormones,
aldosterone and
parathyroid hormone
Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine.
PTH influences bone ...
s. Serious
electrolyte disturbance
Electrolyte imbalance, or water-electrolyte imbalance, is an abnormality in the concentration of electrolytes in the body. Electrolytes play a vital role in maintaining homeostasis in the body. They help to regulate heart and neurological function ...
s, such as
dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
and
overhydration
Water intoxication, also known as water poisoning, hyperhydration, overhydration, or water toxemia, is a potentially fatal disturbance in brain functions that results when the normal balance of electrolytes in the body is pushed outside safe lim ...
, may lead to cardiac and neurological complications and, unless they are rapidly resolved, will result in a
medical emergency
A medical emergency is an acute injury or illness that poses an immediate risk to a person's life or long-term health, sometimes referred to as a situation risking "life or limb". These emergencies may require assistance from another, qualified ...
.
Measurement
Measurement of electrolytes is a commonly performed diagnostic procedure, performed via
blood testing with
ion-selective electrode
An ion-selective electrode (ISE), also known as a specific ion electrode (SIE), is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solution into an electrical potential. The voltage is theoretically dependent ...
s or
urinalysis
Urinalysis, a portmanteau of the words ''urine'' and ''analysis'', is a panel of medical tests that includes physical (macroscopic) examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Macroscopic ...
by
medical technologist
A medical laboratory scientist (MLS) or clinical laboratory scientist (CLS) or medical technologist (MT) performs diagnostic testing of blood and body fluids in clinical laboratories. The scope of a medical laboratory scientist's work begins wit ...
s. The interpretation of these values is somewhat meaningless without analysis of the
clinical history and is often impossible without parallel measurements of
renal function. The electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except for
arterial blood gas
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe an ...
interpretations since they are inherently linked to sodium levels. One important test conducted on urine is the
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...
test to determine the occurrence of an
electrolyte imbalance
Electrolyte imbalance, or water-electrolyte imbalance, is an abnormality in the concentration of electrolytes in the body. Electrolytes play a vital role in maintaining homeostasis in the body. They help to regulate heart and neurological function, ...
.
Rehydration
In
oral rehydration therapy
Oral rehydration therapy (ORT) is a type of fluid replacement used to prevent and treat dehydration, especially due to diarrhea. It involves drinking water with modest amounts of sugar and salts, specifically sodium and potassium. Oral rehydrat ...
, electrolyte drinks containing sodium and potassium salts replenish the body's water and electrolyte concentrations after dehydration caused by
exercise,
excessive alcohol consumption,
diaphoresis
Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals.
Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distribu ...
(heavy sweating), diarrhea, vomiting,
intoxication
Intoxication — or poisoning, especially by an alcoholic or narcotic substance — may refer to:
* Substance intoxication:
** Alcohol intoxication
** LSD intoxication
** Toxidrome
** Tobacco intoxication
** Cannabis intoxication
** Cocaine i ...
or starvation. Athletes exercising in extreme conditions (for three or more hours continuously, e.g. a
marathon or
triathlon
A triathlon is an endurance multisport race consisting of swimming, cycling, and running over various distances. Triathletes compete for fastest overall completion time, racing each segment sequentially with the time transitioning between the ...
) who do not consume electrolytes risk
dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
(or
hyponatremia
Hyponatremia or hyponatraemia is a low concentration of sodium in the blood. It is generally defined as a sodium concentration of less than 135 mmol/L (135 mEq/L), with severe hyponatremia being below 120 mEq/L. Symptoms can be a ...
).
A home-made electrolyte drink can be made by using water, sugar and salt
in precise proportions. It is important to include
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
(sugar) to utilise the co-transport mechanism of sodium and glucose. Commercial preparations are also available for both human and veterinary use.
Electrolytes are commonly found in
fruit juices, sports drinks, milk, nuts, and many fruits and vegetables (whole or in juice form) (e.g., potatoes,
avocado
The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family ( Lauraceae). It is native to the Americas and was first domesticated by Mesoamerican tribes more than 5,000 years ago. Then as now it was prized for ...
s).
Electrochemistry
When
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...
s are placed in an electrolyte and a
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
is applied, the electrolyte will conduct electricity. Lone
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
s normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the
cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...
, providing electrons to the electrolyte. Another reaction occurs at the
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...
, 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.
![Chloralkali membrane](https://upload.wikimedia.org/wikipedia/commons/7/7a/Chloralkali_membrane.svg)
For example, in a solution of ordinary table salt (sodium chloride, NaCl) in water, the cathode reaction will be
:2 H
2O + 2e
− → 2 OH
− + H
2
and
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas will bubble up; the anode reaction is
:2 NaCl → 2 Na
+ + Cl
2 + 2e
−
and
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
gas will be liberated into solution where it reacts with the sodium and hydroxyl ions to produce
sodium hypochlorite
Sodium hypochlorite (commonly known in a dilute solution as bleach) is an inorganic chemical compound with the formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may also be viewed as the sodium s ...
- household
bleach. 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
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 chemica ...
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 to
solvate
Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the ...
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.
* In
batteries, 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.
* In some
fuel cells, a solid electrolyte or
proton conductor
A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ are the primary charge carriers.
Composition
Acid solutions exhibit proton-conductivity, while pure proton conductors are usually dry solids. Typical materials ...
connects the plates electrically while keeping the hydrogen and oxygen fuel gases separated.
* In
electroplating 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 of
mercury 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.
* In
electrolytic capacitors the chemical effect is used to produce an extremely thin
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
or
insulating coating, while the electrolyte layer behaves as one capacitor plate.
* In some
hygrometer
A hair tension dial hygrometer with a nonlinear scale.
A hygrometer is an instrument used to measure the amount of water vapor in air, in soil, or in confined spaces. Humidity measurement instruments usually rely on measurements of some other qu ...
s 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
Solid electrolytes can be mostly divided into four groups described below.
Gel electrolytes
Gel electrolytes – closely resemble liquid electrolytes. In essence, they are liquids in a flexible
lattice framework. Various
additive
Additive may refer to:
Mathematics
* Additive function, a function in number theory
* Additive map, a function that preserves the addition operation
* Additive set-functionn see Sigma additivity
* Additive category, a preadditive category with f ...
s are often applied to increase the
conductivity
Conductivity may refer to:
*Electrical conductivity, a measure of a material's ability to conduct an electric current
**Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution
** Ionic conductivity (solid state), ele ...
of such systems.
Polymer electrolytes
Dry polymer electrolytes – differ from liquid and gel electrolytes in the sense that salt is dissolved directly into the solid medium. Usually it is a relatively high
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
constant
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
(
PEO,
PMMA PMMA may refer to:
* para-Methoxymethamphetamine, a stimulant drug
* Philippine Merchant Marine Academy
The Philippine Merchant Marine Academy ( fil, Akademiya sa Bapor Pangkalakalan ng Pilipinas) also referred to by its acronym PMMA) is a ma ...
,
PAN,
polyphosphazene
Polyphosphazenes include a wide range of hybrid inorganic-organic polymers with a number of different skeletal architectures with the backbone P- N-P-N-P-N-. In nearly all of these materials two organic side groups are attached to each phosphoru ...
s,
siloxane
A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compound ...
s, etc.) and a salt with low
lattice energy
In chemistry, the lattice energy is the energy change upon formation of one mole of a crystalline ionic compound from its constituent ions, which are assumed to initially be in the gaseous state. It is a measure of the cohesive forces that bin ...
. In order to increase the
mechanical strength
The field of strength of materials, also called mechanics of materials, typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the re ...
and conductivity of such electrolytes, very often
composites are used, and inert ceramic phase is introduced. There are two major classes of such electrolytes: polymer-in-ceramic, and ceramic-in-polymer.
Ceramic electrolytes
Solid ceramic electrolytes –
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s migrate through the ceramic phase by means of vacancies or
interstitials within the
lattice
Lattice may refer to:
Arts and design
* Latticework, an ornamental criss-crossed framework, an arrangement of crossing laths or other thin strips of material
* Lattice (music), an organized grid model of pitch ratios
* Lattice (pastry), an orna ...
. There are also glassy-ceramic electrolytes.
Organic plastic electrolytes
Organic ionic plastic crystals – are a type
organic salts exhibiting
mesophase In chemistry and chemical physics, a mesophase is a state of matter intermediate between liquid and solid. Gelatin is a common example of a partially ordered structure in a mesophase. Further, biological structures such as the lipid bilayers of cell ...
s (i.e. a
state of matter
In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many intermediate states are known to exist, such as liquid crystal, ...
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.
They have various forms of disorder due to one or more solid–solid
phase transition
In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...
s below the
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
and have therefore
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
properties and good mechanical flexibility as well as improved electrode, electrolyte interfacial contact. In particular, protic organic ionic plastic crystals (POIPCs),
[
] which are solid
protic
In chemistry, a protic solvent is a solvent that has a hydrogen atom bound to an oxygen (as in a hydroxyl group ), a nitrogen (as in an amine group or ), or fluoride (as in hydrogen fluoride). In general terms, any solvent that contains a labile ...
organic salts formed by
proton transfer from a
Brønsted acid to a Brønsted base and in essence are protic
ionic liquid
An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...
s in the
molten state, have found to be promising solid-state
proton conductor
A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ are the primary charge carriers.
Composition
Acid solutions exhibit proton-conductivity, while pure proton conductors are usually dry solids. Typical materials ...
s for
fuel cells. Examples include
1,2,4-triazolium perfluorobutanesulfonate
Onekama ( ) is a village in Manistee County, Michigan, Manistee County in the U.S. state of Michigan. The population was 411 at the 2010 United States Census, 2010 census. The village is located on the shores of Portage Lake (Michigan), Portage Lak ...
and
imidazolium methanesulfonate.
[
]
See also
*
Strong electrolyte
*
Salt bridge
In electrochemistry, a salt bridge or ion bridge is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell), a type of electrochemical cell. It maintains electrical neutrality within the in ...
*
ITIES
In electrochemistry, ITIES (interface between two immiscible electrolyte solutions) is an electrochemical interface that is either polarisable or polarised. An ITIES is polarisable if one can change the Galvani potential difference, or in other wor ...
(interface between two immiscible electrolyte solutions)
*
Ion transport number
*
Elektrolytdatenbank Regensburg
Elektrolytdatenbank Regensburg (abridged ELDAR) is a compilation of thermodynamic data, bibliography and properties of electrolytes and their solutions.
History
The gathering of data has begun since 1981. It is a member of DECHEMA
DECHEMA is an a ...
*
VTPR VTPR (short for Volume-Translated Peng–Robinson)
is an estimation method for the calculation of phase equilibria of mixtures of chemical components. The original goal for the development of this method was to enable the estimation of properties of ...
*
Electrochemical machining
References
External links
*
*
*
*
{{Use dmy dates, date=April 2017
Blood tests
Urine tests
Physical chemistry
Acid–base physiology