Displacement reaction

A displacement reaction is a chemical reaction in which one substance is displaced from another. In a narrower sense, this term mainly relates to acid-base reactions : In general, the stronger acid (or base ) displaces the weaker acid (or base) from its salt. However, a weaker, non-volatile or non-volatile acid (or base) can also displace a more volatile, stronger acid (or base) from its salt, since this is an equilibrium reaction in which a possibly volatile component is constantly removed from the equilibrium .

The reaction is based on the fact that the solubility product with a strong acid / base i. d. Usually lower than that of a salt compound with a weak acid / base.

Examples: In the detection reaction for acetates, the weak acetic acid is displaced from its salts by strong acids such as sulfuric acid:

{\ displaystyle \ mathrm {CH_ {3} COO ^ {-} + HSO_ {4} ^ {-} \; {\ overrightarrow {\ leftarrow}} CH_ {3} COOH + SO_ {4} ^ {2-}} }

Acetate is protonated by hydrogen sulfate. Acetic acid and sulfate are formed .

The strong acid sulfuric acid releases sulfur dioxide or sulphurous acid from sulphites and hydrogen chloride or hydrochloric acid from chlorides as the weaker acid. Concentrated hydrochloric acid is according to the same principle of displacement of sulfides hydrogen sulfide , and cyanides of hydrogen cyanide free. Caustic soda as a strong base releases the weak base ammonia from amines and ammonium compounds .

Displacement reactions also occur in other areas of chemistry - e.g. B. in complex formation reactions through ligand exchange (the "stronger" complexing agent displaces the weaker one) as well as in adsorption and desorption processes. Adsorption is the accumulation of the sorbent on the surface of the sorbent - a reversible equilibrium process that can be influenced and shifted by changes in concentration, temperature or displacement reactions. Absorption is the irreversible binding, absorption or storage of the sorbent on / by / in the sorbent. Desorption is the opposite process; H. the detachment of adsorbed substances from the sorbent: they are displaced.

Individual evidence

↑ Holleman, Wiberg: Textbook of Inorganic Chemistry. 102nd edition, 2007, ISBN 978-3-11-017770-1 , p. 216.

[1] Holleman, Wiberg: Textbook of Inorganic Chemistry. 102nd edition, 2007, ISBN 978-3-11-017770-1 , p. 216.