An electrolyte is a substance which dissociates free ions when dissolved (or molten), to produce an electrically conductive medium. Because they generally consist of ions in solution, electrolytes are also known as ionic solutes. They are sometimes referred to in abbreviated jargon as lytes.
Electrolytes generally exist as acids, bases or salts.
An electrolyte may be described as concentrated if it has a high concentration of ions; or dilute, a low concentration of ions. If a high proportion of the dissolved solute dissociates to form ions, the solution is strong; if most of the dissolved solute remains un-ionised, the solution is weak.
The properties of electrolytes may be exploited via electrolysis to extract constituent elements and compounds contained within the solution.
In physiology, the primary electrolytes are sodium, potassium, calcium, magnesium, chloride, phosphate, and bicarbonate.
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.
Electrolyte balance is maintained by oral intake of electrolyte-containing substances, and is regulated by hormones, generally with the kidneys flushing out excess levels. In humans, salt homeostasis is regulated by hormones such as antidiuretic hormone, aldosterone and parathyroid hormone. Serious electrolyte disturbances may lead to cardiac and neurological complications, and most are medical emergencies.
Measurement of electrolytes is a commonly performed diagnostic procedure, performed via blood testing or urinalysis. 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, as they are inherently linked to sodium levels.
Electrolyte drinks containing sodium and potassium salts are used to replenish the body's water and electrolyte levels after dehydration caused by exercise, diaphoresis, diarrhea, vomiting or starvation. Giving pure water to such a person is not the best way to restore fluid levels, because it dilutes the salts inside the body's cells and interferes with their chemical functions. This can lead to water intoxication.
Sports drinks such as Gatorade are electrolyte drinks with large amounts of added carbohydrates, such as glucose, to provide energy. The drinks commonly sold to the public are isotonic (with osmolality close to that of blood), with hypotonic (with a lower osmolality) and hypertonic (with a higher osmolality) varieties available to athletes, depending on their nutritional needs.
Because sports drinks contain very high levels of sugar, they are not recommended for regular use in children. Rather, specially formulated pediatric electrolyte solutions are recommended. (Also, dentists recommend that regular consumers of sports drinks observe precautions against tooth decay.)
Electrolyte and sports drinks can be home-made by using the correct proportions of sugar, salt and water.
Uses in Electrochemistry
The behaviour of electrolytes in electrochemistry is discussed further in the electrolysis article.
Electrolytic conductors are used in electronic devices where the chemical action at a metal/electrolyte interface yields useful effects.
- In batteries the effect is used to store energy as chemical fuel on the surface of metal plates, and the electrolyte also serves as a conductor which connects the plates electrically.
- In some fuel cells a solid electrolyte or proton conductor 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' or insulating coating, while the electrolyte layer behaves as one capacitor plate.
- In some hygrometers 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 electric current through it.