Aggregate state of table salt. Table salt, chemistry

More than 10 million organic and more than 500,000 inorganic compounds are known to chemists to date. Among them are complex in structure and properties, which are used only for chemical or medical purposes. And there are those that are not at all complicated and very common in everyday life. But this is no less important and significant. To one of these substances is table salt. In everyday life it is also called food, and in the chemical industry it is called sodium chloride or sodium chloride. In the technological industry, it is called the mineral it forms in nature - halite, as well as rock salt or hard rock salt. Let us consider in more detail the aggregate state of table salt, the structure, properties, extraction, application and history of introduction into mass consumption.

In what states does salt exist?

What is the aggregate state of substances and how does it happen? It depends on what substance is involved. Each student above the 7th grade can call the aggregate state of table salt, because this is the substance that is found in each house. Today, without it, it is difficult for a modern person to imagine his life. In addition, the aggregate state of table salt is quite obvious to the naked eye - small or large dispersed crystals of the correct cubic form. However, dissolving the salt in water, we will get it already in another aggregate state - liquid. We will get the same result if we simply melt the crystals at high temperature. The only condition that is not characteristic for salt is gaseous. But under certain conditions, you can get it.

Conditions for changing the aggregate state

1. To obtain salt in a liquid state by melting solid crystals of natural origin, it is necessary to apply a temperature equal to 800 ^o C.
2. To transfer the salt to the gaseous state, the molten crystals must be brought to a boiling point (about 1400 ° C) and boiled until the structural components are completely transformed into ions (Na ⁺ and CL-).
3. The solid aggregate state of table salt is its natural form in natural conditions.

Why does such a spread of temperatures occur when manipulating crystals? This is explained by the structure of the crystal lattice.

Crystal cell

It is a regular face-centered cubic transparent crystal. In each corner of the cube (lattice sites) there are alternating positively charged Na ⁺ ions and negatively charged ions of CL ^- . Due to the sharply distinguished electronegativity of these atoms, there is such a strong electrostatic attraction between them that severe conditions (high temperature, mechanical impact) must be applied to destroy it. This type of crystal lattice is called ionic, and it is characteristic for all salts of alkaline, alkaline-earth and transition metals.

That is why the temperature of table salt (for both melting and boiling) is so high. However, crystals can be obtained not only in cubic form, but also in pyramidal (eight-, twelve- and twenty-sided) crystals. To do this, simply adjust the evaporation temperature of the salted solution in a certain way. In any case, the internal cavity of the crystals remains filled with liquid, if it is a solution of salt in water.

The chemical formula of sodium chloride is simple and is expressed by the elemental NaCl composition.

Physical properties of halite

The physical properties of sodium chloride can be described in several places:

• Solid crystals of white, pink, blue, purple, red. The color depends on the presence of impurities during extraction. The pure substance is crystal white.
• It dissolves in water in a ratio of approximately 100/30 (in 100 g of water 30 g of salt). The good solubility is due to the presence of water dipoles, which associate ions of sodium and chlorine around them, causing destruction of the electrostatic attraction between them and, as a consequence, destruction of the crystal lattice.
• Melts and boils at high temperatures (800-1400 ^о С).
• Has a subtle pleasant smell.
• Salty on the palate.

Chemical properties of sodium chloride

Like any soluble middle salt, sodium chloride is able to interact with:

• Other salts in the reaction of exchange (mandatory condition: the reaction of gas evolution, precipitation or formation of malodissocompatible substance): NaCL + AgNO ₃ = NaNO ₃ + AgCL (white cheesy precipitate). This is a qualitative reaction to the ion CL ^-.
• With metals, standing in the EHRNM to the left of sodium: K + NaCL = KCL + Na.
• Dissociates in water solution into free hydrated dipoles of water ions: NaCL _(aqueous solution ₎ = Na ⁺ + CL-. As a result, a solution of common salt is formed, which is a strong electrolyte.
• Hydrolysis is not affected, since it is a salt formed by a strong acid and a strong base.
• During electrolysis (the action of electric current) decomposes to form free products and caustic soda (caustic): NaCl = Na + Cl ₂ + NaOH.

Where is sodium chloride found in nature?

At present, table salt is a substance often found in nature. And although it was always so, but in ancient times and times of the Middle Ages it was considered a very expensive product. All this from the fact that they did not know how to extract salt from natural sources. And there are a lot of such sources in world reserves - halite is considered an almost unlimited natural resource. Where is the salt in nature?

1. Seas and oceans with salt water.
2. Salty Lakes.
3. Salted springs.
4. The groundwater.
5. Waters of estuaries.

Extraction of halite

The extraction and processing of salt have their own technology, since simply mined matter is most often unsuitable for use because of the high content of foreign impurities. Obtain a halite differently, for example:

• By underground works;
• From the seams at the bottom of salt ponds;
• Evaporating or freezing out salty sea or ocean water;
• Evaporation of groundwater.

Any of the methods makes it possible to obtain halite crystals. However, for consumption in food they must undergo another kind of treatment - grinding. After all, hardly anyone uses at home cooking a large crystal of table salt. Most often it is purchased in the already purified from impurities, crushed practically in powder form. Also there are kinds of salt iodized, fluorinated and so on, not only for food, but also for technical purposes.

The use of rock salt

Areas of application and use of sodium chloride are very extensive. The main ones, together with examples and results, are listed in the table.

History of appearance in everyday life

Salt appeared on tables in every house not at once. Once it was worth its weight in gold, and in the most direct sense. As early as the 18th century, some peoples of Africa exchanged a handful of salt for a handful of golden sand. A little later in Ethiopia, salt bars were the standard currency. In ancient Rome, military legionaries even gave out a monthly salary with this substance, which eventually led to the naming of their soldiers. Children of poor African peoples simply licked stone pieces of salt as a treat. In Holland, it was used to punish criminals, for torture. The perpetrator was not given salt at all, and the person died in a short time.

For the first time to allocate and consume this substance people have learned in ancient times. Then it was found that the salt is contained in the plants. Therefore, they were burned, and ash was used as a seasoning. Later in China they learned to evaporate salt from sea water, and the process of developing methods of obtaining it began to move faster.

In Russia salt was extracted from lakes (the most famous salty lakes in Russia are still Elton and Baskunchak). Then the commercial importance of the substance was very rare. It was obtained by only a few merchants, who then sold at exorbitant prices. Only rich and famous people could afford to have salt. Over time, production and production have improved. Various methods of extraction and processing began to be used, and to date one of the most common household substances is sodium chloride. The chemistry of this compound, its properties, its application in medicine and other branches became known approximately from the XVI-XVII centuries.

Study in the school course

The study of the structure and the aggregate state, as well as the chemical properties of table salt, begins with the school bench, within the framework of a discipline such as chemistry (grade 8). Salts in the school course are studied in all their diversity in nature. Students get an idea of the chemical basis, empirical formulas, basic physical and chemical properties. For simplicity and convenience of memorizing formulas and physical properties on the flyleaf of the textbook, there are usually salts, the table of which gives an idea of their solubility in water. There you can find information about the solubility of acids, bases and alkalis.

An important characteristic of salts is their fusibility, on the basis of which their extraction in nature is also constructed. It is easy for students to find their bearings when solving problems for salt fusibility. Table and graphic images allow not only to see, fusible substance or refractory, but also to determine the approximate temperature of melting and boiling. Typically, such tables are also located in the textbooks ("Chemistry", 8 class). Salts should be studied in the context of such sciences as biology and physics. Therefore, many tasks for students are built on the integration of intersubject communications.