Electrolyte

Electrolyte

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In chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, an electrolyte is any substance containing free ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s that make the substance electrically conductive
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...

. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible.

Commonly, electrolytes are solutions of acids, bases or salts. Furthermore, some gases may act as electrolytes under conditions of high temperature or low pressure. Electrolyte solutions can also result from the dissolution of some biological (e.g., DNA, polypeptides) and synthetic polymers (e.g., polystyrene sulfonate), termed polyelectrolytes, which contain charged functional groups.

Electrolyte solutions are normally formed when a salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called solvation
Solvation
Solvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...

. For example, when table salt, 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, e.g., carbon dioxide gas dissolves in water to produce a solution which contains hydronium, carbonate, and hydrogen carbonate ions.

Note that molten salts can be electrolytes as well. For instance, when sodium chloride is molten, the liquid conducts electricity.

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
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 to extract constituent elements and compounds contained within the solution.

Physiological importance


In physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

, the primary ions of electrolytes are sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 (Na+), potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 (K+), calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 (Ca2+), magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 (Mg2+), chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

 (Cl), hydrogen phosphate (HPO42−), and hydrogen carbonate (HCO3). The electric charge symbols of plus (+) and minus (−) indicate that the substance in question is ionic in nature and has an imbalanced distribution of electrons, the result of chemical dissociation
Dissociation (chemistry)
Dissociation in chemistry and biochemistry is a general process in which ionic compounds separate or split into smaller particles, ions, or radicals, usually in a reversible manner...

.

All known higher lifeforms require a subtle and complex electrolyte balance between the intracellular
Intracellular
Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

 and extracellular
Extracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...

 environment. In particular, the maintenance of precise osmotic gradients of electrolytes is important. Such gradients affect and regulate the hydration of the body as well as blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

, and are critical for nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

 and muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

 function. Various mechanisms exist in living species that keep the concentrations of different electrolytes under tight control.

Both muscle tissue and neurons are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between the extracellular fluid
Extracellular fluid
Extracellular fluid usually denotes all body fluid outside of cells. The remainder is called intracellular fluid.In some animals, including mammals, the extracellular fluid can be divided into two major subcompartments, interstitial fluid and blood plasma...

 or interstitial fluid
Interstitial fluid
Interstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...

, and intracellular fluid. 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
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...

 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.

Electrolyte balance is maintained by oral, or in emergencies, intravenous (IV) intake of electrolyte-containing substances, and is regulated by hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s, generally with the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s flushing out excess levels. In humans, electrolyte homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

 is regulated by hormones such as antidiuretic hormone, aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...

 and parathyroid hormone
Parathyroid hormone
Parathyroid hormone , parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids...

. Serious electrolyte disturbance
Electrolyte disturbance
Electrolytes play a vital role in maintaining homeostasis within the body. They help to regulate myocardial and neurological function, fluid balance, oxygen delivery, acid-base balance and much more. Electrolyte imbalances can develop by the following mechanisms: excessive ingestion; diminished...

s, such as dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...

 and overhydration
Water intoxication
Water intoxication, also known as water poisoning, is a potentially fatal disturbance in brain functions that results when the normal balance of electrolytes in the body is pushed outside of safe limits by over-consumption of water....

, may lead to cardiac and neurological complications and, unless they are rapidly resolved, will result in a medical emergency
Medical emergency
A medical emergency is an injury or illness that is acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the...

.

Measurement


Measurement of electrolytes is a commonly performed diagnostic procedure, performed via blood test
Blood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....

ing with ion selective electrode
Ion selective electrode
An ion-selective electrode , also known as a specific ion electrode , is a transducer that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or pH meter. The voltage is theoretically dependent on the logarithm of the...

s or urinalysis
Urinalysis
A urinalysis , also known as Routine and Microscopy , is an array of tests performed on urine, and one of the most common methods of medical diagnosis...

 by medical technologist
Medical technologist
A Medical Laboratory Scientist is a healthcare professional who performs chemical, hematological, immunologic, microscopic, and bacteriological diagnostic analyses on body fluids such as blood, urine, sputum, stool, cerebrospinal fluid , peritoneal fluid, pericardial fluid, and synovial...

s. The interpretation of these values is somewhat meaningless without analysis of the clinical history
Medical history
The medical history or anamnesis of a patient is information gained by a physician by asking specific questions, either of the patient or of other people who know the person and can give suitable information , with the aim of obtaining information useful in formulating a diagnosis and providing...

 and is often impossible without parallel measurement of renal function
Renal function
Renal function, in nephrology, is an indication of the state of the kidney and its role in renal physiology. Glomerular filtration rate describes the flow rate of filtered fluid through the kidney...

. Electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except for arterial blood gas
Arterial blood gas
An arterial blood gas is a blood test that is performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or...

 interpretation since they are inherently linked to sodium levels. One important test conducted on urine is the specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 test to determine the occurrence of electrolyte imbalance.

Rehydration


In oral rehydration therapy
Oral rehydration therapy
Oral rehydration therapy is a simple treatment for dehydration associated with diarrhoea, particularly gastroenteritis or gastroenteropathy, such as that caused by cholera or rotavirus. ORT consists of a solution of salts and sugars which is taken by mouth...

, electrolyte drinks containing sodium and potassium salts replenish the body's water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and electrolyte levels after dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...

 caused by exercise, excessive alcohol consumption
Alcohol abuse
Alcohol abuse, as described in the DSM-IV, is a psychiatric diagnosis describing the recurring use of alcoholic beverages despite negative consequences. Alcohol abuse eventually progresses to alcoholism, a condition in which an individual becomes dependent on alcoholic beverages in order to avoid...

, diaphoresis
Diaphoresis
Diaphoresis is excessive sweating commonly associated with shock and other medical emergency conditions.Diaphoretic is the state of perspiring profusely, or something that has the power to cause increased perspiration....

, diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...

, intoxication or starvation
Starvation
Starvation is a severe deficiency in caloric energy, nutrient and vitamin intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death...

. Athletes exercising in extreme conditions (for three or more hours continuously e.g. marathon
Marathon
The marathon is a long-distance running event with an official distance of 42.195 kilometres , that is usually run as a road race...

 or triathlon
Triathlon
A triathlon is a multi-sport event involving the completion of three continuous and sequential endurance events. While many variations of the sport exist, triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances...

) who do not consume electrolytes risk dehydration (or hyponatremia
Hyponatremia
Hyponatremia is an electrolyte disturbance in which the sodium concentration in the serum is lower than normal. In the vast majority of cases, hyponatremia occurs as a result of excess body water diluting the serum sodium and is not due to sodium deficiency. Sodium is the dominant extracellular...

).

A simple electrolyte drink can be home-made by using the correct proportions of water, sugar, salt, salt substitute for potassium, and baking soda.

Electrolytes are commonly found in fruit juices, coconut water
Coconut water
Coconut water is the clear liquid inside young coconuts . As the fruit matures, the coconut water is gradually replaced by the coconut meat and air. A very young coconut has very little meat; the meat that it has is very tender, almost a gel...

, sports drink
Sports drink
A sports drink beverage is designed to help athletes rehydrate when fluids are depleted after training or competition. Electrolyte replacement promotes proper rehydration, which is important in delaying the onset of fatigue during exercise...

s, milk, and many fruits and vegetables (whole or in juice form) (e.g. potatoes, avocados).

Electrochemistry


When electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s are placed in an electrolyte and a voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 is applied, the electrolyte will conduct electricity. Lone electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

 consuming electrons from the anode. Another reaction occurs at the anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

, producing electrons that are eventually transferred to the cathode. 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.

For example, in a solution of ordinary table salt (sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

, NaCl) in water, the cathode reaction will be
2H2O + 2e → 2OH + H2

and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas will bubble up; the anode reaction is
2NaCl → 2 Na+ + Cl2 + 2e

and chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 gas will be liberated. The positively charged sodium ions Na+ will react towards the cathode neutralizing the negative charge of OH there, and the negatively charged hydroxide ions OH will react towards 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
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 of H+ and OH through water to the other electrode takes longer than movement of the much more prevalent salt ions.

Also: Electrolytes dissociate in water because water molecules are dipoles and the dipoles orient in an energetically favorable manner to solvate 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
    Battery (electricity)
    An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

    , two metal
    Metal
    A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

    s 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 cell
    Fuel cell
    A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...

    s, a solid electrolyte or proton conductor
    Proton conductor
    A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ are the primary charge carriers.-Composition:For practical applications, proton conductors are usually solid materials. Typical materials are polymers or ceramic. Typically the pores in practical materials are small...

     connects the plates electrically while keeping the hydrogen and oxygen fuel gases separated.
  • In electroplating
    Electroplating
    Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...

     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
    Mercury (element)
    Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

     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 capacitor
    Electrolytic capacitor
    An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics"...

    s the chemical effect is used to produce an extremely thin 'dielectric
    Dielectric
    A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...

    ' or insulating
    Electrical insulation
    thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

     coating, while the electrolyte layer behaves as one capacitor plate.
  • In some hygrometer
    Hygrometer
    A hygrometer is an instrument used for measuring the moisture content in the environmental air, or humidity. Most measurement devices usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed...

    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.

See also

  • Strong electrolyte
    Strong electrolyte
    A strong electrolyte is a solute that completely, or almost completely, ionizes or dissociates in a solution. These ions are good conductors of electric current in the solution....

  • ITIES
    ITIES
    ITIES is an acronym used in electrochemistry for the "Interface between Two Immiscible Electrolyte Solutions". Usually, one electrolyte is an aqueous electrolyte composed of hydrophilic ions such as NaCl dissolved in water and the other electrolyte is a lipophilic salt such as tetrabutylammonium...

    (Interface between Two Immiscible Electrolyte Solutions)