Salt (chemistry)

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Crystal structure of the NaCl.

Potassium dicromato salt has the bright orange color characteristic of dicromato anion.

In chemistry, a salt is a chemical compound formed by cations (positively charged ions) linked to anions (negatively charged ions) by an ionic bond. They are the typical product of a chemical reaction between a base and an acid, where the base provides the cation and the acid the anion.

The chemical combination between an acid and a hydroxide (base) or an oxide and a hydronium (acid) produces a more liquid salt, which is called neutralization.

An example is table salt, colloquially called common salt or sea salt. It is the specific salt sodium chloride. Its molecular formula is NaCl and it is the product of the base sodium hydroxide (NaOH) and hydrochloric acid, HCl.

In general, salts are ionic compounds that form crystals. They are generally soluble in water, where the two ions separate. Typical salts have a high melting point, low hardness, and low compressibility. Melted or dissolved in water, they conduct electricity.

Lomonosov in his Works on Chemistry and Physics described the concept of "salt" as follows:

The name of the salt denotes fragile bodies dissolved in water and remains transparent; they do not turn on if, in their pure form, they are exposed to the fire. Its types: vitriolo and all other metal salts, alumbre, bórax, tartar, essential plant salts, tartar salt and potassium, volatile urine salt, salitre, common spring salt, sea salt and rock, ammonia, Epsom salt and other salts obtained as a result of chemical work.

Training

Salts are formed by a chemical reaction between:

A base and an acid, for example, NH₃ + HCl → NH₄Cl
A metal and acid, for example, Mg + H₂SO₄ → MgSO₄ + H₂+o
A metal and a non-metal, for example, Ca + Cl₂ → CaCl₂
A base and an acid anhydride, for example, 2 NaOH + Cl₂O → 2 NaClO + H₂O
An acid and an anhydrated base, for example, 2 HNO₃ + Na₂O → 2 Nano₃ + H₂O

Salts can also be formed if solutions of different salts are mixed, their ions recombine, and the new salt is insoluble and precipitates (see: solubility equilibrium), for example:

Pb (NO₃) 2 + Na₂SO4 → PbSO₄ ↓ + 2 NaNO₃

Nomenclature

According to traditional nomenclature, salts are named by the name of the anion, with a certain prefix and suffix, followed by the preposition of and the name of the cation. We must distinguish between different cases:

In the hydraulic salts, the termination is replaced - Hydra. from which the anion comes for termination -uro.. For example, NaCl is sodium chloride; Cl anion^- comes from HCl (chloric acid).
In oxo acid salts, termination is replaced - That's it. or- Boy. of the oxa acid from which the anion comes - Ito or -ato.. For example, the Ca₃(PO)₄)₂ is the calcium phosphate; the PO anion₄^3- comes from the H₃PO₄ (phosphoric acid).H+OH-
Acid salts (salals that come from polyprótic acids and containing substitute hydrogen atoms) are called indicating the number of unsubstituted hydrogens remaining in the molecule, using the corresponding prefix. For example, NaHS is sodium hydrogenosulfure; HS anion^- comes from sulfuric acid.
Basic salts (salals containing hydroxyl ions, OH^-) are named indicating the number of hydroxyl followed by the central anion and finally the cathion. For example, MgCl (OH) is magnesium hydroxychloride.
Hydrated salts (containing crystallization water) are called indicating the corresponding salt and then the number of molecules that ask to be toxic and non-toxic.

Types of salt

Salts can be classified in various ways. Salts that produce hydroxide ions when dissolved in water are called alkali salts. Salts that produce acidic solutions are acidic salts. Neutral salts are those salts that are neither acidic nor basic. Zwitterions contain an anionic and cationic center in the same molecule, but they are not considered salts. Examples of zwitterions include amino acids, many metabolites, peptides, and proteins.

If we consider salts as substitution products of cations in acids or hydroxo groups in bases, then the following types of salts can be distinguished:

Medium salts (normal) are the products of the substitution of all hydrogen cations of acid molecules by metal cationes (Na2CO3, K3PO4).
Acid salts are products of partial substitution of hydrogen cations in acids with metal cationes. The acid salts are a kind of salts that produce an acid solution after being dissolved in a solvent. Its formation as a substance has greater electrical conductivity than that of pure solvent.
Basic salts are products of incomplete substitution of basic hydroxy groups (OHs)^-)  for acid residues ₂CO₃. They are formed in conditions of excess base or lack of acid.
Complex Sales Na₂[Zn(OH)₄

Depending on the number of cations and anions present in the structure, the following types of salts are distinguished:

Simple salts: salts consisting of a type of cation and a type of anion: NaCl
Double salts are salts containing two different cationes: (SO4)2·12 H2O
Mixed salts are salts containing two different anions: Ca(OCl)Cl or whitening lime.

Also distinguish between hydrate salts (crystalline hydrates), which include water of crystallization molecules e.g. Na₂SO₄ 10 H₂O and complex salts containing a complex cation or complex anion K₄[Fe(CN)₆] The inner salts are made up of zwitterionic ions i.e. molecules containing positively charged and negatively charged atoms.

Properties

Physical properties

The dependence on the solubility of some salts regarding temperature.

In general, salts are crystalline materials with an ionic structure. For example, halide crystals of alkaline and alkaline earth metals (NaCl, CsCl, CaF2) formed by anions, located at the beginning of the densest spherical packing, and cations that occupy holes within the package. Ionic salt crystals can also be formed from acid residues combined in endless anionic dimensional structures and fragments of these with cations in the cavities (such as silicates). This structure is appropriately reflected in their physical properties: they have high melting points and in the solid state they are dielectric.

Also known are salts of molecular (covalent) structure (for example, aluminum chloride AlCl₃) In many salts, the nature of the chemical bonds is intermediate between ionic and covalent.

Of particular interest are ionic liquids, with melting points below 100 °C. During the abnormal melting of ionic liquids there is practically no vapor pressure, but a high viscosity. The special properties of these salts are explained by the low symmetry of the cation, the weak interaction between the ions and a good distribution of the cation charge.

Colour

Potassium dicromato, a bright orange salt used as a pigment.

manganese dioxide, opaque black salt.

Salts can appear to be clear and transparent (like sodium chloride), opaque, and even metallic and shiny (like pyrite or iron sulfide). In many cases the apparent opacity or transparency is related to the difference in size of the individual single crystals; Since light reflects off grain boundaries, large crystals tend to be transparent, whereas polycrystalline aggregates have the appearance of white powder.

Salts can be many different colors. Some examples are:

Yellow (sodium throat)
Orange (potassium scromato)
Red (potassium cryanide)
Malva (cobalt chloride (II))
Blue (Copper Sulphate (II), Prussian blue)
Lila (potassium permanganate)
Green (Nickel chloride (II))
White (magnesium sulphate)
Black (manganese oxide (IV))
No color (sodium chloride)

Most inorganic minerals and pigments, as well as many synthetic organic dyes, are salts. The color of the specific salt is due to the presence of unpaired electrons in the atomic orbital of the transition elements.

Taste

Different salts can cause all five different basic tastes, such as salty (sodium chloride), sweet (lead(II) acetate, which causes lead poisoning if ingested), sour (lead(II) bitartrate), potassium), bitter (magnesium sulfate) and umami (monosodium glutamate).

Smell

Salts of strong acids and strong bases (strong salts) are usually involatile and odorless, while salts of both weak bases and weak acids (weak salt) may have an odor in the conjugate acid form (for example, acetates like acetic acid or vinegar, and cyanides like hydrogen cyanide in almonds) or in the conjugate base form (for example, ammonium salts like ammonia) of the component ions. This partial and slow decomposition is usually accelerated in the presence of water, since hydrolysis is the other half of the equation of the reversible reaction for the formation of weak salts.

Melting Point

Salts characteristically have high melting points. For example, sodium chloride melts at 801°C. Some salts with low lattice energies are liquid at or near room temperature. These include molten salts, which are often mixtures of salts, and ionic liquids, which typically contain organic cations. These liquids have unusual properties as solvents.

Solubility

Many ionic compounds exhibit significant solubility in water or other polar solvents. Unlike molecular compounds, salts dissociate in solution into anionic and cationic components. The lattice energy, the cohesive forces between these ions within a solid, determines solubility. Solubility depends on how well each ion interacts with the solvent, so certain patterns become apparent. For example, sodium, potassium, and ammonium salts are often soluble in water. Notable exceptions include ammonium hexachloroplatinate and potassium cobaltinitrite. Most nitrates and many sulfates are soluble in water. Exceptions include barium sulfate, calcium sulfate (sparingly soluble), and lead(II) sulfate, where the 2+/2− pairing leads to high lattice energies. For similar reasons, most metal carbonates are not soluble in water. Some soluble carbonate salts are: sodium carbonate, potassium carbonate, and ammonium carbonate.

Conductivity

Salts are characteristic insulators. Molten salts or salt solutions conduct electricity. For this reason, liquefied (molten) salts and solutions containing dissolved salts (for example, sodium chloride in water) can be used as electrolytes.

Chemical Properties

Chemical properties are determined by the properties of cations and anions or a part of them.

Salts react with acids and bases, obtaining the reaction product and a gas, precipitate or a substance such as water

$mathsf{BaCl_2 + H_2SO_4 longrightarrow BaSO_4downarrow + 2 HCl}$

$mathsf{NaHCO_3 + HCl longrightarrow NaCl + H_2O + CO_2 uparrow}$

$mathsf{Na_2SiO_3 + 2 HCl longrightarrow 2 NaCl + H_2SiO_3 downarrow}$

Salts react with metals when the metal is released from the metal salt in an electrochemical series of reactivity:

$mathsf{Cu + HgCl_2 longrightarrow CuCl_2 + Hg}$

The salts react with each other and the product resulting from the reaction (they produce gas, and precipitate sediment or water); these reactions can take place with the change in the oxidation states of the reactive atoms:

$mathsf{CaCl_2 + Na_2CO_3 longrightarrow CaCO_3 downarrow + 2 NaCl}$

$mathsf{AgNO_3 + NaCl longrightarrow AgCl downarrow + NaNO_3}$

$mathsf{K_2Cr_2O_7 + 3 Na_2SO_3 + 4 H_2SO_4 longrightarrow Cr_2(SO_4)_3 + 3 Na_2SO_4 + K_2SO_4 + 4 H_2O}$

Some salts decompose when heated:

$mathsf{CuCO_3 longrightarrow CuO + CO_2 uparrow}$

$mathsf{Ca(NO_3)_2 longrightarrow Ca(NO_2)_2 + O_2uparrow }$

$mathsf{NH_4NO_3 longrightarrow N_2O uparrow + 2 H_2O}$

$mathsf{NH_4NO_2 longrightarrow N_2 uparrow + 2 H_2O}$

Dissolutions

Salts are strong electrolytes. When diluted in water they dissociate completely, in a reaction called hydrolysis. It generally affects the pH of the solution.

The salt dissolutions that come from a strong acid and a strong base form a neutral dissolution. For example, the dissolution of sodium nitrate: ${displaystyle {mathsf {NaNO_{3}longrightarrow Na^{+}+NO_{3}^{-}}}}$

In this kind of reaction, the pH of the solution is close to seven.

Dissolutions of salts from a strong base and a weak acid are basic, which means they have a pH greater than seven. As an example we find the dissolution of the sodium acetate: ${displaystyle {mathsf {CH_{3}COONalongrightarrow Na^{+}+2CH_{3}COO^{-}}}}$

On the contrary, the salt dissolutions of a weak base and a strong acid are acid, and the resulting pH is less than seven. An example is the dissolution of the ammonium chloride: ${displaystyle {mathsf {Nh_{4}Cllongrightarrow NH_{4}^{+}+Cl^{-}}}}$ Generally, all metal ions produce acidic dissolutions.

If the solution occurs with a salt from a weak base and weak acid, then the result will depend on the relative strengths of the reaction. This behavior can be predicted by the dissociation constant.

Come out strong

Strong salts or strong electrolyte salts are chemical salts made up of strong electrolytes. These ionic compounds completely dissociate in water. They are generally odorless and nonvolatile.

Strong salts begin with Na__, K__, NH₄__, or end with __NO₃, __ClO₄, or __CH₃COO. Most of the group 1 and 2 metals form strong salts. Strong salts are especially useful when creating conductive compounds, as their constituent ions allow for higher conductivity.

Weak Salt

Weak salts or "weak electrolyte salts" they are, as the name suggests, composed of weak electrolytes. They are generally more volatile than strong salts. They may have an odor similar to the acid or base from which they are derived. For example, sodium acetate, NaCH₃COO, smells similar to acetic acid CH₃COOH.

Training

Solid lead (II) sulfate (PbSO₄)

Salts are formed by a chemical reaction between:

A base and an acid, for example, NH3 + HCl → NH4Cl
A metal and acid, for example, Mg + H2SO4 → MgSO4 + H2
A metal and a non-metal, for example, Ca + Cl2 → CaCl2
A base and an acid anhydride, for example, 2 NaOH + Cl2O → 2 NaClO + H2O
An acid and an anhydrous base, for example,2 HNO3 + Na2O → 2 NaNO3 + H2O

In the salt metathesis reaction, in which two different salts are mixed in water, their ions recombine and the new salt is insoluble and precipitates. For example:

Pb(NO)₃)₂ + Na₂SO₄ → PbSO₄↓ + 2 NaNO₃

Classifications

Salts can be classified into the following groups:

Haloid salt, hydraulic or neutral binary: they are binary compounds formed by a metal and a non-metal, without any other element. The anion will always have the termination -uro.. Examples: sodium chloride, NaCl; iron chloride (III), FeCl₃Iron sulfide (II), FeS.
Oxacid salt: it comes from replacing the hydrogens of an oxacid by metal cations.
- Oxácida, oxiacida or neutral ternaria: all hydrogens are replaced. Example: Sodium hypochlorite, NaClO.
- Acid salt: part of the hydrogens are replaced. Example: sodium hydrogenocarbonate or sodium bicarbonate, NaHCO₃.
- Basic or hydroxysal salt: containing hydroxide ions (OH)^-) besides other anions. They can be classified as salts or hydroxides. Example: iron hydroxycarbonate (III), Fe(OH)CO₃.
- Double salt: hydrogens are replaced by two or more cations. Example: double potassium and lithium carbonate, KLiCO₃.
Hydroxosal: salt formed from an abnormal hydroxide, which reacts as an acid a weak base to a base or a strong acid.

Al(OH)₃ + 3 Na(OH) → Al(OH)₆Na₃ (hexahydroxyaluminate sodium)

Al(OH)₃ + 3 HCl → AlCl₃ (Aluminum chloride) + 3 H₂O

Mixed salt: contains several anions. Examples: calcium chloridefluoride, CaClF; potassium chlorophosphate, K₄ClPO₄, iron nitratesulphate (III), Fe(NO₃SO₄.
Oxisal: formed by the union of oxide and salt. Examples: lead oxinitrate (IV), PbO(NO)₃)₂cobalt oxychloride (III), CoOCl.
Moisturized salt or hydrate: salt with water molecules in its crystalline structure. Examples: lead oxide (II) hemihydrate (or hemihydrated), PbO·1⁄2H₂O; dihydrate calcium sulfate, CaSO₄·2H₂Or.

As can be seen in the classification above, both halide salts and oxacid salts are called “neutral salts”. Natural salts are the ones we commonly know.

Location

Salts are found either as a mineral as part of rocks (such as halite), or dissolved in water (for example, seawater). They are a vital component of living beings, in which we can find them in different ways:

Dissolved within the organisms in the ions that constitute them, which can act in certain biological processes:
- Transmission of nerve impulses
- Muscle contracting
- Synthesis and activity of chlorophyll
- Transport of oxygen from hemoglobin
- Cofactors that help enzymes
Forming part of solid insoluble structures that provide protection or support (bones, shells...)
Associated with organic molecules: there are ions that are essential for the synthesis of some biomolecules (e.g. iodine for hormones manufactured in the thyroid gland), or for certain functions (e.g., ion phosphate associated with lipids forms the phospholipids of the cell membrane; phosphoproteins such as the caseine of milk, the hemogloin...

Saline solutions

A saline solution is the result of a strong acid reaction with a strong base. It is highly ionized and therefore neutral. The explanation is that the against ions of strong acids and weak bases are fairly stable, and therefore do not hydrolyze the water. An example would be sodium chloride, lithium bromide and others.
A saline solution of a strong acid with a weak base is acid. This is because, after dissociating the salt when dissolved, the weak base tends to grasp OH-, hydroxides that will get hydrolysing the water. Finally, we have an excess of hydronio ions in dissolution that give acidity to dissolution. The weaker the base, the more acidic the resulting dissolution.
Chemistry: A saline solution of a weak acid with a strong base is basic. The mechanism is the same as in the previous case: the acid, being weak, will tend to capture a proton, which must necessarily proceed from water hydrolysis. An example, the water dissolution of the sodium acetate.
Commonly it is called saline solution to the mixture of common salt (NaCl) and water, in this mixture the salt

Application of salts

Salts are ubiquitous in both manufacturing and everyday life.

Cryric acid salts. Of the chlorides the most used are sodium chloride and potassium chloride.
Sodium chloride (table salt)) is extracted from lakes and sea water and is also extracted from salt mines. Cooking salt is used in food. In industry, sodium chloride serves as a raw material for chloroa, sodium hydroxide and sodium acid carbonate.
Potassium chloride is used in agriculture as potassium fertilizer.
Sulfuric acid salts In the construction and medicine much is used in the semiaquatic plaster obtained by cooking the rock (dehydrated calcium sulphate). When mixed with water, it solidifies quickly to form dihydrate calcium sulfate, that is, plaster.
Decahydrated sulfate is used as raw material for soda production.
Nitrates are the most used nitrates as fertilizers in agriculture. The most important are sodium nitrate, potassium nitrate, calcium nitrate and ammonium nitrate. These salts are usually called salitre.
Of orthophosphates, the most important is calcium orthophosphate. This salt is the main constituent of phosphorous and apatite minerals. Phosphorous and apatite are used as raw materials in the production of phosphate fertilizers, such as superphosphate and precipitate.
Carbonic acid salts Calcium carbonate is used as the raw material for the production of lime.
Sodium carbonate (sosa) is used in the production of glass and in the cooking of soaps.
Calcium carbonate is also naturally found as limestone, chalk and marble.