# electrolyte

An electrolyte (masculine, from ancient Greek ἤλεκτρον electron , German 'amber' , figuratively 'electric' and λυτικός lytikós , German 'dissolvable' ) is a chemical compound that is dissociated into ions in a solid, liquid or dissolved state and which moves directed under the influence of an electric field . The solid or liquid material that contains the mobile ions is often referred to as electrolyte . The electrical conductivity of such ion conductors is lower than is typical for metals . They are therefore referred to as 2nd class leaders .

First class conductors (with electrons as charge carriers ) in contact with an ion conductor are called electrodes . Electrochemical reactions occur at the interfaces , especially when current flows .

Electrolytes are vital for the body and its water balance. A lack of electrolytes, often together with a lack of fluids, quickly leads to heat damage, sometimes life-threatening .

## Classification

In the broadest sense, electrolytes are substances that are at least partially present as ions. A distinction is made between

• dissolved electrolytes
• strong electrolytes that break completely into ions when dissolved, such as sodium chloride .
• weak electrolytes that only partially dissociate in solution, such as acetic acid .

For the conductivity of dissolved electrolytes see electrolytic conductivity .

Examples:
NaCl ( s ) → Na + ( aq ) + Cl - (aq)
NaOH (s) → Na + (aq) + OH - (aq)
• In the case of a potential electrolyte, on the other hand, the ions only arise through the reaction with the solvent.
Example:
HCl ( g ) + H 2 O → Cl - (aq) + H 3 O + (aq)

The most important electrolytes are therefore either acids , bases or salts .

## liquids

Electrolytes in the sense of ion conductors require mobile ions. Therefore, all liquids that contain ions are electrolytes. Liquid electrolytes are molten salts and ionic liquids as well as all liquid solutions of ions. Molten salts and ionic liquids usually only consist of ions, but they can contain dissolved molecules. In the case of aqueous or organic electrolyte solutions, it is the other way round: Here the solvent consists of molecules and the ions are dissolved in it. The production of an electrolyte solution can consist in the simple dissolution of already existing ions, or in a chemical reaction in which ions are formed, for example an acid-base reaction such as the dissolution of molecules such as hydrogen chloride or ammonia in water . Information about the translational mobility of ions in the electrolyte solution, such as their diffusion coefficient or their mobility in an electric field, can be obtained using field gradient NMR methods. The measure but can also with the "traditional method" of the "moving interface" ( moving interface done). ${\ displaystyle \ mu}$${\ displaystyle \ mu}$

## Solid

Also solids may contain mobile ions. Especially at high temperatures, ions become mobile in solids consisting of ions, for example. But there are also solid electrolytes that can be used at room temperature or at only slightly elevated temperatures. This also includes the polymer electrolyte membranes used in some fuel cells . They consist of a plastic framework that contains ionic side groups. Some sodium aluminates , for example, are important ion conductors . In addition to their use in fuel cells, solid electrolytes are also important in sensors , such as the lambda probe , which contains an electrolyte that conducts oxygen ions (e.g. YSZ , yttria stabilized zirconia , a mixture of zirconium dioxide ZrO 2 and yttrium oxide Y 2 O 3 ). The Nernst lamp, commonly used as an incandescent lamp around 1900, also used such solid electrolytes.

## Biological electrolytes

The most important ions of biological electrolytes are sodium , potassium , calcium , magnesium , chloride , phosphate and hydrogen carbonate , and in plants also nitrates . They are contained in the cytosol and are indispensable for the function of the cells and the conduction of stimuli, but also for the membrane potential . Other ions are necessary as trace elements for the cell, but the ions mentioned are particularly important with regard to the electrolyte balance of the cell, since they play an outstanding role in regulating the osmotic pressure .

## physiology

cation function Concentration [mmol / l]
intraz. interst. plasma
sodium extracellular osmolarity, action potential 15th 143 141
potassium intracellular osmolarity, resting membrane potential 140 4th 4th
Calcium second messenger , bone remodeling 0.0001 1.3 2.5
magnesium cellular excitability 15th 0.7 1
Anion function Concentration [mmol / l]
intraz. interst. plasma
chloride 8th 115 103
Bicarbonate Acid-base balance 15th 28 25th
phosphate intracellular buffer 60 1 1
sulfate 10 0.5 0.5
organic acids 2 5 4th
1. freely solved part
2. about 1.3 mmol / l freely dissolved, the rest complexed
3. about 1 mmol / l freely dissolved, the rest organically bound

Even the earliest protozoa let pure water flow unhindered across their cell membranes, while strictly regulating their electrolyte content; They could always rely on constant concentrations in the seawater, their external environment . The cells of the land-living multicellular cells (including humans) continue to work according to this principle, but the ocean is no longer available to them, rather the organism must also control the concentrations in the extracellular fluid, the inner milieu , by regulating intake (eating behavior and Keep absorption in the intestine ) and excretion (reabsorption in the kidneys ) constant.

From the free passage of water it follows that its distribution is determined by the distribution of osmotically active substances (the majority of which are electrolytes), because different osmotic concentrations generate different osmotic pressures that drive the water towards the higher osmolarity. The osmolarity in the human body is around 300 mosmol / l both intracellularly and extracellularly; it is kept constant by controlling the absorption and excretion of water . The sodium content determines the volume of the extracellular fluid and thus also the blood volume , which is kept constant for circulatory stability.

If you lose a lot of salt and water through profuse sweating or diarrhea, it is not enough just to add the water again, because water without salt lowers the osmolarity so that the water is excreted again to maintain osmo homeostasis . Full electrolyte solutions are clinically infused to treat volume deficiency. Sports drinks that advertise isotonicity are usually not suitable for correcting a real volume deficiency, because they achieve the osmolarity of the body mainly through sugar, which is quickly removed from the blood by blood sugar regulation , leaving a hypotonic solution; however, no isotonic drink is necessary, as more water than salt is lost through sweat.

Disorders of the hormones or organs involved in electrolyte homeostasis manifest themselves in characteristic electrolyte disorders . If a causal therapy is not possible, it can be treated by infusing suitable solutions, diuretics , dietary supplements or avoiding certain foods. The most powerful therapy is dialysis .

## Electrochemical Applications

An important application of electrolytes is in electrolysis, including electroplating . Electrolytes are also necessary components of batteries , accumulators and electrolytic capacitors . For the origin of the term electrolyte coined by Michael Faraday , see also “ Faraday's Laws ”, for the meaning of the electrolyte concentration, see also Nernst equation .

### Galvanic electrolytes

The following electrolytes are used in electroplating.

## literature

• Carl H. Hamann, Wolf Vielstich: Electrochemistry I. Electrolytic conductivity, potentials, phase boundaries . 2nd Edition. VCH Verlagsgesellschaft mbH, Oldenburg and Bonn 1985, ISBN 3-527-21100-4 .