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. For example, when table salt, NaCl, is placed in water, the following occurs:
It is also possible for substances to react with water when they are added to it, producing ions, e.g. carbon dioxide gas dissolves in water to produce a solution which contains hydrogen ions and bicarbonate ions.
In simple terms, the electrolyte is a material that dissolves in water to give a solution that conducts an electric current.
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 to extract constituent elements and compounds contained within the solution.
In physiology, the primary ions of electrolytes are sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (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, which is the result of chemical dissociation.
All higher lifeforms require a subtle and complex electrolyte balance between the intracellular and extracellular milieu. In particular, the maintenance of precise osmotic gradients of electrolytes is important. Such gradients affect and regulate the hydration of the body, blood pH, 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 neurons are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between the extracellular fluid or interstitial 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 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 hormones, generally with the kidneys flushing out excess levels. In humans, electrolyte homeostasis is regulated by hormones such as antidiuretic hormone, aldosterone and parathyroid hormone. Serious electrolyte disturbances, such as dehydration and overhydration, may lead to cardiac and neurological complications and, unless they are rapidly resolved, will result in a medical emergency.
Measurement of electrolytes is a commonly performed diagnostic procedure, performed via blood testing with ion selective electrodes or urinalysis by medical technologists. The interpretation of these values is somewhat meaningless without analysis of the clinical history and is often impossible without parallel measurement of renal function. Electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except for arterial blood gas interpretation since they are inherently linked to sodium levels. One important test conducted on urine is the specific gravity test to determine the occurrence of electrolyte imbalance.
Electrolytes are commonly found in sports drinks. In oral rehydration therapy, electrolyte drinks containing sodium and potassium salts replenish the body's water and electrolyte levels after dehydration caused by exercise, diaphoresis, diarrhea, vomiting, intoxication or starvation.
"It is unnecessary to replace losses of sodium, potassium and other electrolytes during exercise since it is unlikely that a significant depletion of the body's stores of these minerals will occur during normal training. However, in extreme exercising conditions over 5 or 6 hours (an Ironman or ultramarathon, for example) the consumption of a complex sports drink with electrolytes is recommended."(-Elizabeth Quinn, trainer and health professional) Athletes who do not consume electrolytes under these conditions risk overhydration (or hyponatremia).
Because sports drinks typically contain very high levels of sugar, they are not recommended for regular use by children. Water is considered the only essential beverage for children during exercise. Medicinal rehydration sachets and drinks are available to replace the key electrolyte ions lost during diarrhea and other gastro-intestinal distresses. Dentists recommend that regular consumers of sports drinks observe precautions against tooth decay.
When electrodes are placed in an electrolyte and a voltage is applied, the electrolyte will conduct electricity. Lone electrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode consuming electrons from the cathode, and another reaction occurs at the anode producing electrons to be taken up by the anode. 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 move to neutralize these charges so that the reactions can continue and the electrons can keep flowing.
For example, in a solution of ordinary salt (sodium chloride, NaCl) in water, the cathode reaction will be
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.