Salt is sodium chloride, used as an additive to food, a food preservative. It is also used in the chemical industry, medicine. Serves as the most important raw material for caustic soda, hydrochloric acid, soda and other substances. The formula for sodium chloride is NaCl.
Formation of an ionic bond between sodium and chlorine
The chemical composition of sodium chloride reflects the conventional formula NaCl, which gives an idea of the equal number of sodium and chlorine atoms. But the substance is not formed by diatomic molecules, but consists of crystals. In the interaction of an alkali metal with a strong non-metal, each sodium atom gives off a valence electron to a more electronegative chlorine. Sodium cations Na + and anions of the acid residue of hydrochloric acid Cl - arise. Opposite charged particles are attracted, forming a substance with an ionic crystal lattice. Small sodium cations are located between large chlorine anions. The number of positive particles in the composition of sodium chloride is equal to the number of negative, the substance as a whole is neutral.
Chemical formula. Salt and Halite
Salts are complex substances of ionic structure, the names of which begin with the name of the acid residue. The formula for sodium chloride is NaCl. Geologists call a mineral of this composition “halite”, and sedimentary rock - “rock salt”. An outdated chemical term that is often used in production is “sodium chloride”. This substance is known to people from ancient times, once it was considered "white gold". When reading school equations involving sodium chloride, modern school and college students call chemical signs (“sodium chlorine”).
We carry out simple calculations according to the formula of the substance:
1) Mr (NaCl) = Ar (Na) + Ar (Cl) = 22.99 + 35.45 = 58.44.
The relative molecular weight is 58.44 (in amu).
2) The molar mass is numerically equal to the molecular weight, but this value has units of measurement g / mol: M (NaCl) = 58.44 g / mol.
3) A 100 g salt sample contains 60.663 g of chlorine atoms and 39.337 g of sodium.
Physical properties of salt
Fragile halite crystals are colorless or white. In nature, there are also deposits of rock salt, painted in gray, yellow or blue. Sometimes a mineral substance has a red tint, which is due to the types and amount of impurities. The hardness of halite on the Mohs scale is only 2-2.5, glass leaves a dash on its surface.
Other physical parameters of sodium chloride:
- smell is absent;
- taste is salty;
- density - 2.165 g / cm3 (20 ° C);
- melting point - 801 ° C;
- boiling point - 1413 ° C;
- solubility in water - 359 g / l (25 ° C);
Obtaining sodium chloride in the laboratory
When metallic sodium interacts with gaseous chlorine in a test tube, a white substance is formed - sodium chloride NaCl (sodium chloride formula).
Chemistry gives an idea of the different methods for producing the same compound. Here are some examples:
The neutralization reaction: NaOH (aq.) + HCl = NaCl + H 2 O.
Redox reaction between metal and acid:
2Na + 2HCl = 2NaCl + H 2 .
The effect of the acid on the metal oxide: Na 2 O + 2HCl (aq.) = 2NaCl + H 2 O
Displacement of a weak acid from a solution of its salt with a stronger one:
Na 2 CO 3 + 2HCl (aq) = 2NaCl + H 2 O + CO 2 (gas).
For industrial use, all of these methods are too expensive and complicated.
Salt production
Even at the dawn of civilization, people knew that after salting, meat and fish last longer. Transparent, regular-shaped halite crystals were used in some ancient countries instead of money and were worth their weight in gold. The search and development of halite deposits made it possible to satisfy the growing needs of the population and industry. The most important natural sources of salt:
- halite mineral deposits in different countries;
- water of the seas, oceans and salt lakes;
- interlayers and crusts of rock salt on the banks of salty water bodies;
- halite crystals on the walls of volcanic craters;
- salt flats.
The industry uses four main methods for producing table salt:
- leaching of halite from the underground layer, evaporation of the resulting brine;
- mining in salt mines ;
- evaporation of sea water or brine of salt lakes (sodium chloride accounts for 77% of the mass of dry residue);
- use of salt water desalination by-product.
Chemical properties of sodium chloride
In its composition, NaCl is an average salt formed by alkali and soluble acid. Sodium chloride is a strong electrolyte. The attraction between the ions is so great that only strongly polar solvents can destroy it. In water, the
ionic crystal lattice of a substance decays, cations and anions (Na
+ , Cl
- ) are released. Their presence is due to the electrical conductivity, which has a solution of sodium chloride. The formula in this case is written in the same way as for dry matter - NaCl. One of the qualitative reactions to sodium cation is the staining of the burner flame yellow. To get the result of the experiment, you need to collect a little hard salt on a clean wire loop and add it to the middle part of the flame. The properties of salt are also associated with the feature of the anion, which consists in a qualitative reaction to chloride ion. When interacting with silver nitrate, a white precipitate of silver chloride precipitates in the solution (photo). Hydrogen chloride is displaced from the salt by stronger acids than hydrochloric: 2NaCl + H
2 SO
4 = Na
2 SO
4 + 2HCl. Under normal conditions, sodium chloride does not undergo hydrolysis.
Scopes of rock salt
Sodium chloride lowers the melting point of ice, so in winter, a mixture of salt and sand is used on roads and sidewalks. It absorbs a large amount of impurities; when melted, it pollutes rivers and streams. Road salt also accelerates the process of corrosion of car bodies, damages trees planted next to roads. In the chemical industry, sodium chloride is used as raw material for a large group of chemicals:
- of hydrochloric acid;
- sodium metal;
- chlorine gas;
- caustic soda and other compounds.
In addition, salt is used in the manufacture of soaps and dyes. As a food antiseptic is used in canning, salting of mushrooms, fish and vegetables. To combat disorders of the thyroid gland in the population, the salt formula is enriched by the addition of safe iodine compounds, for example, KIO 3 , KI, NaI. Such supplements support the production of thyroid hormone and prevent endemic goiter.
The value of sodium chloride for the human body
The formula of table salt, its composition has acquired vital importance for human health. Sodium ions are involved in the transmission of nerve impulses. Chlorine anions are necessary for the production of hydrochloric acid in the stomach. But too much salt in food can lead to high blood pressure and an increased risk of heart and vascular disease. In medicine, with large blood loss, patients are injected with physiological saline. To obtain it, 9 g of sodium chloride are dissolved in one liter of distilled water. The human body needs a continuous supply of this substance with food. Salt is excreted through the excretory organs and skin. The average sodium chloride content in the human body is approximately 200 g. Europeans consume about 2-6 g of table salt per day, in hot countries this figure is higher due to higher sweating.