Autoprotolysis

The proteolysis (or proteolytic reaction ) is a chemical reaction in which a proton ( H ion ) is transmitted between two reactants. The term protolysis is often described incorrectly the elimination of protons. The protolysis is the key operation on the key Brønstedschen acid-base theory. Then an acid transmits a proton (H ) to a reactant. Known as acid compound acts as a proton donor ( proton donor ), the base (often water) takes the protons and is therefore referred to as a proton acceptor. Between the reactants to a chemical equilibrium is established.

Protolytic reactions

If the gas is hydrogen chloride ( HCl ) is introduced into water, formed under protolysis the hydrochloric acid. In this equilibrium reaction is the molecule HCl and the H3O ion proton donors, ie after Brønsted acids. H2O and Cl act as proton acceptors, they are after so Brønsted bases.

For example, pure acetic acid ( H3C -COOH ) in water, formed under protolysis H3O and the acetate anion ( H3C -COO- ). Here are CH3COOH and H3O proton donors, while H3C -COO- and H2O are proton acceptors.

Protolysis the dibasic compound sulfuric acid in water:

In this equation, the molecules H2SO4 and H3O ion proton donors, ie after Brønsted acids. H2O SO42 - and act as proton acceptors, they are after so Brønsted bases. Plays a special role HSO4 - which can react as a proton acceptor or proton donor depending on the reaction direction. This is known substances with such properties as ampholytes.

If the gas is ammonia (NH3 ) was introduced into water, ammonium ions ( NH4 ) and hydroxide ions form (OH - ). Proton donors are here NH4 and H2O, while OH and NH3 are proton acceptors.

Autoprotolysis

Pure water is subject to a so-called autoionization. This produces hydronium ions ( H3O ) and hydroxide ions (OH - ). H2O can react both as a proton donor ( an acid ) or as a proton acceptor ( as the base). We therefore speak here of an ampholyte.

The balance is very much on the side of the water. The ionic product of this reaction is about 10-14 mol2 L-2 at 298 K (25 ° C). The autoionization of water is the reason that even chemically pure water has a low electrical conductivity at least. An application of the autoprotolysis of electric charge separation is given by the Kelvin - generator when it is operated with chemically pure water.

The autoionization (and therefore pH) is strongly temperature dependent. So be the ion products of water ( in mol2 l -2):

Autoionization in non-aqueous solutions

In Brønstedschen acid -base reactions in addition to water, other sufficiently polar solvents can be used as a reactant, such as methanol or ethanol. A good example is the autoionization of liquid ammonia. They form the ammonium ion and amide.

Ion product = 10-32

Even in concentrated sulfuric acid are analogous reactions known:

Ion product = 10-4

Also of hydrogen fluoride:

Ion product = 10 to 10.7 (0 ° C)

(For more examples under ampholyte # Examples of ampholytes. )

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