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Salt

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

   A magnified crystal of a salt (halite/sodium chloride)
   Enlarge
   A magnified crystal of a salt ( halite/ sodium chloride)

   A salt, in chemistry, is any ionic compound composed of cations
   (positively charged ions) and anions (negative ions) so that the
   product is neutral (without a net charge). These component ions can be
   inorganic (Cl^−) as well as organic (CH[3]COO^−) and monoatomic
   ions(F^−) as well as polyatomic ions (SO[4]^2−); they are formed when
   acids and bases react.

   There are several varieties of salts: Normal salts are those that do
   not contain a hydroxide ion (OH^−) or a hydrogen ion (H^+). Salts that
   contain a hydroxide ion are basic salts and salts that contain a
   hydrogen ion are acid salts. Impure salts is a name for salts which
   have lost their saltiness, and can also refer to natrons. Zwitterions
   are salts that contain an anionic center and a cationic centre in the
   same molecule; examples include amino acids, many metabolites, peptides
   and proteins.

   When salts are dissolved in water, they are called electrolytes, and
   are able to conduct electricity, a property that is shared with molten
   salts. Mixtures of many different ions in solution—like in the
   cytoplasm of cells, in blood, urine, plant saps and mineral waters—
   usually do not form defined salts after evaporation of the water.
   Therefore, their salt content is given for the respective ions.

   Salts can be dehydrating to the human body if consumed in excess.

History

   The first registers of salt use were produced around 4000 B.C.
   (roughly) in Egypt, Greece and Rome. Salt was very valuable and used to
   preserve and flavor foods. In Ancient Rome, salt started to be used as
   money originating the current Latin-derivative term salary.
   Unfortunately for those paid with salt, it was easily ruined by rain
   and other factors. Payments to Roman workers were made in salt. Salt
   was also given to the parents of the groom in marriage until the 8th
   century.

   The Phoenicians were the first people to harvest salt from the sea.
   They sold it to other civilizations and most of the time it cost more
   than gold . The Phoenicians were victims of their success and as a
   result of harvesting the salt from the sea, the value of salt
   depreciated. The Phoenicians harvested the salt by flooding plains of
   land with seawater, then leaving the plains to dry. After the water
   dried, the salt which was left was collected and sold.

Appearance

Consistency

   Salts are usually solid crystals with a relatively high melting point.
   However, there exist salts that are liquid at room temperature,
   so-called ionic liquids. Inorganic salts usually have a low hardness
   and a low compressibility, similar to edible salt.

Colour

   Salts can be clear and transparent ( sodium chloride), opaque (
   titanium dioxide), and even metallic and lustrous (iron disulfide).

   Salts exist in all different colors, e.g. yellow (sodium chromate),
   orange ( potassium dichromate), red ( mercury sulfide), mauve ( cobalt
   chloride hexahydrate), blue ( copper sulfate pentahydrate, ferric
   hexacyanoferrate), green ( nickel oxide), colorless ( magnesium
   sulfate), white ( titanium dioxide), and black ( manganese dioxide).
   Most minerals and inorganic pigments as well as many synthetic organic
   dyes are salts.

Taste

   Different salts can elicit all five basic tastes, e.g. salty ( sodium
   chloride), sweet ( lead diacetate ), sour ( potassium bitartrate),
   bitter ( magnesium sulfate), and umami or savory ( monosodium
   glutamate).

Odour

   Pure salts are non- volatile and odorless, while impure salts may smell
   after the conjugate acid (e.g. acetates like acetic acid ( vinegar) and
   cyanides like hydrogen cyanide (almonds) or the conjugate base (e.g.
   ammonium salts like ammonia) of the component ions.

Nomenclature

   Various salt minerals
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   Various salt minerals
   Chemical composition of sea salt
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   Chemical composition of sea salt

   The name of a salt starts with the name of the cation (e.g. sodium or
   ammonium) followed by the name of the anion (e.g. chloride or acetate).
   Salts are often referred to only by the name of the cation (e.g. sodium
   salt or ammonium salt) or by the name of the anion (e.g. chloride or
   acetate).

   Common salt-forming cations include:
     * ammonium NH[4]^+
     * calcium Ca^2+
     * iron Fe^2+ and Fe ^3+
     * magnesium Mg^2+
     * potassium K^+
     * pyridinium C[5]H[5]NH^+
     * quaternary ammonium NR[4]^+
     * sodium Na^+

   Common salt-forming anions (and the name of the parent acids in
   parentheses) include:
     * acetate CH[3]COO^− (acetic acid)
     * carbonate CO[3]^2− ( carbonic acid)
     * chloride Cl^− (hydrochloric acid)
     * citrate HOC(COO^−)(CH[2]COO^−)[2] ( citric acid)
     * cyanide C≡N^− ( hydrogen cyanide)
     * hydroxide OH^− ( water)
     * nitrate NO[3]^− ( nitric acid)
     * nitrite NO[2]^− ( nitrous acid)
     * oxide O^2− ( water)
     * phosphate PO[4]^3− ( phosphoric acid)
     * sulfate SO[4]^2− (sulfuric acid)

Formation

   Salts are formed by a chemical reaction between:
     * A base and an acid, e.g. NH[3] + HCl → NH[4]Cl.

     * A metal and an acid, e.g. Mg + H[2]SO[4] → MgSO[4] + H[2].

     * A base and an acid anhydride, e.g. 2 NaOH + Cl[2]O → 2 NaClO +
       H[2]O

     * An acid and an basic anhydride, e.g. 2 HNO[3] + Na[2]O → 2 NaNO[3]
       + H[2]O

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

   Retrieved from " http://en.wikipedia.org/wiki/Salt"
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   with only minor checks and changes (see www.wikipedia.org for details
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