Salt, the most commonly known of which is sodium chloride, or table salt, is a compound formed by the chemical reaction of an acid with a base. During this reaction, the acid and base are neutralized producing salt, water and heat. Sodium chloride, is distributed throughout nature as deposits on land created by the evaporation of ancient seas and is also dissolved in the oceans. Salt is an important compound with many uses including food preservation, soap production, and de-icing roads and walkways. It is also the primary source of chlorine and sodium for industrial chemicals.
In terms of chemistry, a salt can be any compound formed by the reaction of an acid with a base. Energy, in the form of heat, is given off during this neutralization reaction so it is said to be exothermic. The most common salt, sodium chloride (NaCl), is a product of the reaction between hydrochloric acid (HCl) and the base sodium hydroxide (NaOH). In this reaction, positively charged hydrogen ions (H+) from the acid are attracted to negatively charged hydroxyl ions (OH-) from the base. These ions combine and form water. After the water forms, the sodium and chlorine ions remain dissolved and the acid and base are said to be neutralized. Solid salt is formed when the water evaporates and the negatively charged chlorine ions combine with the positively charged sodium ions.
Solid sodium chloride exists in the form of tiny, cube-shaped particles called crystals. These crystals are colorless, have a density of 2.165 g/cm3 and melt at 1,472°F (800.8°C). They also dissolve in water, separating into the component sodium and chlorine ions. This process known as ionization is important to many industrial chemical reactions.
Common salt (sodium chloride) is found throughout nature. It is dissolved in the oceans with an average concentration of 2.68%. On land, thick salt deposits, formed by the evaporation of prehistoric oceans, are widely distributed. These deposits are true sedimentary rocks and are referred to as rock salt or halite.
People obtain salt from the environment in many different ways. Solid salt deposits are mined directly as rock salt and purified. Salt from sea water is isolated by solar evaporation. Underground salt deposits are solution-mined. This type of mining involves pumping water underground to dissolve the salt deposit, recovering the water with salt dissolved in it, and evaporating the water to isolate the salt.
Beyond being essential to the survival of most plants and animals, salt is also used extensively in many industries. In the food industry it is used to preserve meats and fish because it can slow down the growth of unhealthy microorganisms. It is also used to improve the flavor of many foods. In the cosmetic industry it is used to make soaps and shampoos. In other chemical industries it is the primary source of sodium and chlorine which are both raw materials used for various chemical reactions. Salt is used when manufacturing paper, rubber, and ceramics. And it is commonly used for de-icing roads during the winter.
See also Acids and bases.