Salt formation reaction

Salt formation reactions are various chemical reactions that result in a salt as a product . In order to produce a certain salt, one has to look for reactants that supply the two components of a salt. This includes a cation (metal, ammonium ion ) and an anion of an acid.

The production of a salt is more complicated when several different anions and cations are contained in one salt.

Neutralization of acid and alkali

During neutralization, an alkali reacts with an acid to form salt and water . The components in the acid ( oxonium ions ) and the lye ( hydroxide ions ), which make up their acidic and alkaline properties, react with each other to form water.

Caution: Strongly concentrated solutions can heat up so much during neutralization that the solution can splash.

General equation of reaction

${\displaystyle \mathrm {S{\ddot {a}}ure+Lauge\longrightarrow Salz+Wasser} }$

example 1

Hydrochloric acid + sodium hydroxide solution → sodium chloride + water

${\displaystyle \mathrm {HCl_{(aq)}+NaOH_{(aq)}\longrightarrow NaCl_{(aq)}+H_{2}O_{(l)}} }$

Example 2

Sulfuric acid + barium hydroxide → barium sulfate + water

${\displaystyle \mathrm {H_{2}SO_{4(aq)}+Ba(OH)_{2(aq)}\longrightarrow BaSO_{4(s)}+2\ H_{2}O_{(l)}} }$

Synthesis from the elements

A binary salt (consists of a metal ion and a non-metal ion) can be produced by a direct reaction of the two elements. A redox reaction takes place with the transfer of electrons from the metal to the non-metal. The reaction can be very violent.

General equation of reaction

${\displaystyle \mathrm {Metall+Nichtmetall\longrightarrow Salz} }$

example 1

Sodium + chlorine → sodium chloride

${\displaystyle \mathrm {2\ Na+Cl_{2}\longrightarrow 2\ NaCl} }$

Example 2

Magnesium + iodine → magnesium iodide

${\displaystyle \mathrm {Mg+I_{2}\longrightarrow MgI_{2}} }$

The ion transition from sodium to chloride is actually endothermic, but since the entire reaction is exothermic, other reactions must also play a role in salt formation: the sublimation energy, ionization energy , binding energy , electron affinity and lattice energy .

Metal with acid

If the metal is not too noble, it reacts with an acid, releasing hydrogen . This can arise because electrons are transferred from metal atoms to the oxonium ions of the acid. The anions created in this way form the salt with the metal ions during evaporation .

General equation of reaction

${\displaystyle \mathrm {(unedles)\ Metall+S{\ddot {a}}ure\longrightarrow Salz+Wasserstoff} }$

example

Magnesium + hydrochloric acid → magnesium chloride + hydrogen

${\displaystyle \mathrm {Mg+2\ HCl_{(aq)}\longrightarrow MgCl_{2(aq)}+H_{2(g)}} }$

Index: (aq) indicates that it is HCl (= hydrochloric acid ) dissolved in water .

Metal oxide with acid

Many metal oxides also react with acids. In contrast to the reaction of metals with acids, there is no redox reaction here. It is a rearrangement. Several water molecules are created from the oxygen in the oxide and oxonium ions.

General equation of reaction

${\displaystyle \mathrm {Metalloxid+S{\ddot {a}}ure\longrightarrow Salz+Wasser} }$

example 1

Sodium oxide + hydrochloric acid → sodium chloride + water

${\displaystyle \mathrm {Na_{2}O+2\ HCl\longrightarrow 2\ NaCl+H_{2}O} }$

Example 2

Copper (II) oxide + sulfuric acid → copper sulfate + water

${\displaystyle \mathrm {CuO+H_{2}SO_{4}\longrightarrow CuSO_{4}+H_{2}O} }$

Non-metal oxide with lye

According to the above reaction, oxides of non-metals combine with alkalis to form salts:

General equation of reaction

${\displaystyle \mathrm {Nichtmetalloxid+Lauge\longrightarrow Salz+Wasser} }$

example

Carbon dioxide + calcium hydroxide → calcium carbonate + water

${\displaystyle \mathrm {CO_{2}+Ca(OH)_{2}\longrightarrow CaCO_{3}+H_{2}O} }$

Note: Basically, the options from non-metal oxide and lye or metal oxide with acid correspond to those from acid and lye, since non-metal oxides form acids with water and metal oxides form lyes with water.

Salt with acid

According to the principle ... The stronger acid drives the weaker ones out of their salt ¹ or The less volatile acid drives the more volatile ones out of their salts ² ... you can also make another salt from a salt and an acid.

General equation of reaction

Salt + stronger acid → salt of stronger acid + weaker acid ¹ or

Salt + semi-volatile acid → salt of semi-volatile acid + volatile acid ²

Example for ¹

Sodium carbonate + hydrochloric acid → sodium chloride + carbonic acid

${\displaystyle \mathrm {Na_{2}CO_{3}+2\ HCl\longrightarrow 2\ NaCl+H_{2}CO_{3}} }$

Examples for ²

Potassium bromide + phosphoric acid → potassium dihydrogen phosphate + hydrogen bromide

${\displaystyle \mathrm {KBr+H_{3}PO_{4}\longrightarrow KH_{2}PO_{4}+HBr} }$

This reaction only takes place at an elevated temperature at which the hydrogen bromide escapes from the mixture. At even higher temperatures, the dihydrogen phosphate ion can also react in the same way.

Sodium chloride + sulfuric acid → sodium sulfate + hydrogen chloride

${\displaystyle \mathrm {2\ NaCl+H_{2}SO_{4}\longrightarrow 2\ HCl+Na_{2}SO_{4}} }$

This reaction is an example in which according to the Le Chatelier's principle by the pK _S forth stronger acid value is displaced because of its greater volatility from its salt. It is one of the oldest methods of synthesizing hydrogen chloride ( Kipp's method ).

Salt with salt

In an aqueous solution, two salts can "exchange" ions. This creates two new salts. However, this only works under the condition that one of the two salts formed is sparingly soluble in water. It forms a precipitate. Another possibility is the formation of a double salt when two single salt solutions are mixed. These double salts are often less soluble and crystallize out after mixing.

General equation of reaction

Saline solution A + saline solution B → saline (solution) C + saline solution D

or

Saline A + Saline B → Saline (solution) C

example

Sodium chloride + silver nitrate → silver chloride + sodium nitrate

${\displaystyle \mathrm {NaCl_{(aq)}+AgNO_{3(aq)}\longrightarrow AgCl_{(s)}+NaNO_{3(aq)}} }$

Example double salt

Aluminum sulfate + potassium sulfate → potassium-aluminum-alum

${\displaystyle \mathrm {Al_{2}(SO_{4})_{3(aq)}+K_{2}SO_{4(aq)}+24\ H_{2}O\longrightarrow 2\ KAl(SO_{4})_{2}\cdot 12\ H_{2}O_{(s)}} }$

Uses: The color or solubility of the precipitate in certain substances can be used to identify anions or cations based on such reactions ( quantitative analysis ). Applications for these double salts are given under alums .

Formation of organic salts

Guanidinium hydrochloride - example of a hydrohalide

Tetramethylammonium iodide - example of a tetraalkylammonium salt

There are also a variety of salt formation reactions in organic chemistry :

• Hydrohalides ( hydrofluorides , hydrochlorides , hydrobromides or hydroiodides ) are formed by the reaction of hydrogen halides ( hydrogen fluoride , hydrogen chloride , hydrogen bromide or hydrogen iodide ) with organic amines or amino acids .
• Alcoholates are formed by the reaction of alcohols with alkali or alkaline earth metals.
• Thio alcoholates ( thiolates ) are formed by the reaction of thiols with alkali or alkaline earth metals.
• Enolates are formed from enols under basic conditions .
• Phenolates are formed from phenols by reaction with alkali metals or hydroxides .
• Oxonium salts are formed from alcohols or ethers by reaction with acids.
• Pyridinium salts are formed when pyridine reacts with acids.
• Tetraalkylammonium salts arise from the reaction of trialkylamines with reactive haloalkanes , such as. B. methyl iodide .
• Soaps are formed when fats or oils are saponified with alkali or alkaline earth metal hydroxides.
• Alkylbenolsulfonates (anion-active surfactants ) are formed when the alkylbenolsulfonic acids react with alkali metal hydroxides.
• Triphenylchloromethane can occur as a salt from the triphenylmethyl cation and chloride as an anion (see also triphenylmethane dyes ).
• N -acylimminium chlorides are formed by the chemical reaction of imines with acyl chlorides (= carboxylic acid chlorides ).

Individual evidence

1. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, pp. 1225-1226.
2. ↑ Joachim Buddrus: Fundamentals of Organic Chemistry , 4th edition, de Gruyter Verlag, Berlin, 2011, p. 310, ISBN 978-3-11-024894-4 .
3. ^ Hans Beyer and Wolfgang Walter : Organische Chemie , S. Hirzel Verlag, Stuttgart, 1984, pages 462-463, ISBN 3-7776-0406-2 .
4. ^ Siegfried Hauptmann : Organic Chemistry , 2nd Edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, pp. 739–740, ISBN 3-342-00280-8 .
5. ^ Siegfried Hauptmann : Organic Chemistry , 2nd Edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, p. 741, ISBN 3-342-00280-8 .
6. ↑ Ivan Ernest: Binding, Structure and Reaction Mechanisms in Organic Chemistry , Springer-Verlag, 1972, p. 49, ISBN 3-211-81060-9 .
7. ^ W. Schwarze , K. Drauz, J. Martens: Reaction of 3-thiazolines with carboxylic acid chlorides , Chemiker-Zeitung 1987, 111, 149-153.

Web links

Wikibooks: Inorganic Chemistry for Students / Ions, Salts, Precipitation Reactions and Ion Binding  - Learning and Teaching Materials