Acid-base reaction

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Acid-base reactions according to Brønsted are chemical reactions in which hydrogen cations H + ( protons ) between molecules or molecular ions to be transferred. Because in this type of reaction a particle "detaches" a proton that is taken up by another particle, this reaction is also called protolysis . According to Brønsted , the particle that gives off the proton is called Brønsted acid or proton donor . The particle that receives the proton is called the Brønsted base or proton acceptor .

If a Brønsted acid is represented by the symbol HA and a Brønsted base by B, an acid-base reaction according to Brønsted can be formulated as follows:

Acid + base is in equilibrium with the conjugated (corresponding) base + conjugated (corresponding) acid

There are also other acid-base concepts . Lewis acids and Lewis bases are particularly important.


Acid-base reactions can be broken down into two partial reactions, both of which are referred to as protolysis :

  1. Proton release:
  2. Proton uptake:

Hydrochloric acid is formed when hydrogen chloride gas is dissolved in water . The ampholyte water serves as the base.

In this example, HCl gives off an H + and thus becomes Cl - . The free H + is taken up by H 2 O, which then becomes H 3 O + .

In the other case: ammonia reacts with the ampholyte water, which now functions as an acid, to form a basic solution.


Reaction of hydrochloric acid and ammonia (neutralization)
Adding ammonia water to hydrochloric acid

A special case of the acid-base reaction is neutralization , in which an acidic solution reacts with a basic solution to form a neutral solution. The actual neutralizing reaction consists in the fact that oxonium (hydronium) ions of the acid react as proton donors with hydroxide ions of the base as proton acceptors to form neutral water:

Another example: Hydrogen chloride gas reacts with ammonia gas to form solid ammonium chloride ( salmia ).


In an acid-base titration , a measured acidic or basic sample solution from a burette is mixed with a standard solution of known concentration in order to determine the unknown concentration of the sample solution. A sudden increase in the titration curve or a change in color of the indicator shows that the equivalence or end point of the titration has been reached.


  • Charles E. Mortimer, Johannes Beck and Ulrich Müller: Chemistry. The basic knowledge of chemistry. 11th edition. Thieme, Stuttgart [a. a.] 2014, ISBN 978-3134843118 .

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