Sodium tetraborate (borax) - Na2B4O7

Sodium tetraborate

(“borax”, “borax” (from Latin borax), sodium tetraborate) is an inorganic compound, sodium salt of boric acid with the chemical formula Na 2 B 4 O 7 {\displaystyle {\ce {Na2B4O7}}}, the most common and The boron compound used forms several crystalline hydrates and is widely used in industry.

Being in nature[ | ]

There are numerous minerals containing sodium tetraborate. These include:

• borax (borax, tinkal) - a mineral of the composition Na 2 B 4 O 7 ⋅ 10 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O}}} - sodium tetraborate decahydrate;
• kernite - sodium tetraborate tetrahydrate - Na 2 B 4 O 7 ⋅ 4 H 2 O {\displaystyle {\ce {Na2B4O7.4H2O}}} ;
• numerous minerals of the borate class, which in addition to sodium and boron oxides contain other metals - calcium, magnesium, iron, etc.;
• Sodium tetraborate crystalline hydrates precipitate when some endorheic, seasonally dry salt lakes dry up, such as Lake Searles, located in the Mojave Desert in the United States, and some lakes in Turkey.

Etymology

English word bora

romanized: Middle English form was
bora
, from Old French bora, burra. It may have been from Medieval Latin Baurach (another English spelling), borac (-/um/em), boerau, together with Spanish borrax (> Borraj) and Italian Borrace, in the 9th century. Another name for borax is tincal, from Sanskrit.[12]

The word tinkal

/ˈtɪŋkəl/ “to ring”, or
tinkar
/ˈtɪŋkər/ “Tinker” refers to unrefined borax, before its purification, mined from lake sediments in Tibet, Persia and other parts of Asia. The word was borrowed in the 17th century from Malay. tingkal and from Urdu / Persian / Arabic تنکار‎ tinkar / tankar; thus two forms in English. All this is similar to Sanskrit टांकण Shankana.[19][20]

Chemical properties[ | ]

Solubility in water is 3.2 g / 100 ml (at 25 °C), 10.5 g / 100 ml (at 50 °C), in ethanol - 0.05 g / 100 g (at 25 °C), acetone - 0.006 g / 100 g (at 25 °C), insoluble in diethyl ether and glycerin. Reacts with methanol upon dissolution to form organoboron compounds[2].

Forms several crystalline hydrates with different water contents. These crystalline hydrates and anhydrous sodium tetraborate Na 2 B 4 O 7 {\displaystyle {\ce {Na2B4O7}}} are usually called “borax”. Examples of crystalline hydrates:

• pentahydrate (Na 2 B 4 O 7 ⋅ 5 H 2 O {\displaystyle {\ce {Na2B4O7.5H2O}}}), the so-called “jewelry borax”, is used in soldering jewelry;
• decahydrate ( Na 2 B 4 O 7 ⋅ 10 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O}}} ).

However, the decahydrate Na 2 B 4 O 7 ⋅ 10 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O}}} is most often called “brown”. This salt is transparent crystals with a molar mass of 381.43 g/mol, having good solubility in warm water [4]. When heated above 400 °C, it completely loses water of crystallization.

Since sodium tetraborate is a salt of a weak acid and a strong base, it hydrolyzes in water. An aqueous solution of sodium tetraborate has an alkaline reaction.

Reacts with strong acids, forming the corresponding salt and boric acid:

Na 2 B 4 O 7 ⋅ 10 H 2 O + 2 HCl ⟶ 4 H 3 BO 3 + 2 NaCl + 5 H 2 O {\displaystyle {\ce {Na2B4O7.10H2O + 2 HCl -> 4 H3BO3 + 2 NaCl + 5 H2O}}} .

Many metal salts of boric acid are insoluble in water and when their soluble salts react with sodium tetraborate in a solution, the resulting borates precipitate. This is the basis for the use of borax to “soften” water:

Ca ( aq ) 2 + + Na 2 B 4 O 7 ( aq ) ⟶ CaB 4 O 7 ( s ) + 2 Na ( aq ) + {\displaystyle {\ce {Ca^2+_{(aq)}\ + Na2B4O7_{(aq)}-> CaB4O7_{(s)}\ + 2 Na^+_{(aq)}}}}, Mg ( aq ) 2 + + Na 2 B 4 O 7 ( aq ) ⟶ MgB 4 O 7 ( s ) + 2 Na ( aq ) + {\displaystyle {\ce {Mg^{2}+_{(aq)}\ +Na2B4O7_{(}aq)->MgB4O7_{(s)}\ +2Na_{ (aq)}^{+}}}} .

When fused with the oxides of many transition metals, borax forms variously colored compounds - borates “borax pearls”. The color of the pearls can be used to judge the qualitative chemical composition of the sample.

The compound colors the burner flame green (a characteristic reaction to boron compounds)[4].

Area of ​​application of borax

This substance has found a wide range of applications and is actively used in various industries:

• In industry. In welding production it is used as a component of flux. It is also used for the production of glaze, glass and enamel. In mechanical engineering, this substance is used for the production of antifreeze, lubricants and brake fluids. For disinsection (insect control) at home, it is used as a toxic substance.
• In the textile industry. Treat the surface of the fabric before dyeing.
• In jewelry production. It is used as a flux for soldering metals. It is used to clean the surface of the metal so that the connection is strong. It is used when working with brass, silver and gold.
• In medicine. In this area, this substance is used to combat fungi. For this purpose, preparations from borax in glycerin are prescribed. It is considered a high-quality antiseptic, not inferior in its characteristics to copper sulfate and tannin. It can also be found in pharmacies as a solution of boric acid.
• In cosmetology. This substance is included in almost all cosmetic products. This is explained by its ability to soften hard water and serve as a preservative that extends the shelf life of masks, creams, shower gels, shampoos, etc.
• In soap making. This substance is found in bath bombs. This product owes its effervescent effect to the borax contained in it.

Use of borax in everyday life

This substance is actively used not only in production, but also in everyday life, in some cases it turns out to be irreplaceable. It is used as:

• All-purpose detergent. To do this, take two teaspoons of borax and dissolve them in two glasses of water. Store the substance in a closed container and add small amounts to water when cleaning furniture, washing floors, and windows.
• Insect and rodent control products. Many people know the good old method, passed down from generation to generation, with balls of potato or egg yolk and boric acid. For domestic insects, such a ball serves as real poison. With this method, it is important that insects do not have access to water, otherwise all efforts will be in vain. To control rodents, the powder is scattered along the baseboard on the floor.
• Mold control products. Due to excess moisture and evaporation, mold often appears in the bathroom. This substance will come to the rescue here too. This product can only be used on surfaces without paint, otherwise it will simply peel off. Borax is mixed with water to form a thick, paste-like consistency. Simply apply the mixture in a thick layer to the mold and leave overnight. In the morning, the mixture is removed from the surface, leaving the walls clean.
• Products to combat rust and limescale. Sometimes even expensive products cannot cope with limescale on the sink or toilet. This substance will help in this case too. For this purpose, it is recommended to pour a glass of borax into the toilet bowl and clean the earthenware with a brush in the morning. All stubborn stains will disappear without leaving a trace.

You can buy borax at a pharmacy under the name “Boric acid solution” . The powder can be purchased at a hardware store or searched online on specialized sites.

A kilogram of borax for technical purposes will cost about 150-200 rubles. In large quantities it can be purchased in packs of 25 kg. The pharmacy chain sells an aqueous solution. Its cost can vary from 14 to 100 rubles, depending on the region of residence. It is bottled in bottles with a capacity of 30 to 100 milliliters.

Application[ | ]

Sodium tetraborate is used:

• as a raw material for the production of boric acid and various boron compounds[2];
• in the production of enamels, glazes, optical and colored glasses, various ceramics[2];
• when soldering and melting metals containing flux[2];
• when forging metals;
• in the paper and pharmaceutical industries;
• in the production of building materials as an antiseptic component for the production of cellulose insulation "Ecowool"
• as a disinfectant and preservative[2];
• for preparing buffer solutions;
• in analytical chemistry: as a standard substance for determining the concentration of acid solutions;
• for qualitative determination of metal oxides (by the color of pearls);

In 1977, global production of sodium tetraborate was 1.5 million tons[2].

Flaws

• After use, a deposit of salts forms, which must be removed mechanically;
• It is necessary to choose storage areas that are free of moisture, since high humidity will cause the flux to deteriorate;
• To prepare the material for use, you need to spend time and choose the right proportion, which can lead to errors.

Varieties of Borax

There are two main varieties that relate to the appearance of the material. The first option is the solid form. Borax soldering flux is supplied in the form of a powder with fine solid fractions. Thanks to this, it is easy to lay it on the metal surface before soldering in the required quantity and it will not spread at the same time. This variety is supplied in a special box that protects the material hermetically from the penetration of moisture and other foreign factors. Fractions are white.

Soldering borax in powder form

The second type, which is more often used for lighter metals and their alloys, is diluted borax. In this case, you are offered the same material, but dissolved in liquid. Due to this, it can be used at lower soldering temperatures. Using this type is also easier, since small parts are simply dipped into the liquid, after which they can be soldered. This is used both in the jewelry industry and in other places where small items are worked. Contacts, wires and other types of equipment come into good contact with dissolved flux. Despite the fact that the principle of using borax for soldering in liquid form is somewhat different from the standard one, they have almost the same effect.

There are also varieties in the form of mixtures, when other fluxes are also used. This is necessary in cases where it is impossible to achieve the desired results using one substance. Proportions and composition depend on specific goals. Most often it is combined with boric acid.

Composition and physicochemical properties

The composition of borax for soldering includes sodium chloride and barium chloride, in some cases boric acid is added to it. It is not used in its pure form for all procedures, since this would require too high a melting point. Drill soldering powder is a high-temperature flux, so its main property is resistance to high temperatures. It is worth noting that the material perfectly retains its chemical properties even at a lower concentration than what is supplied. Thus, the flux solution has a fairly high level of dissolution of the oxides of all base metals for which it is used.

It can also dissolve fatty films and other unnecessary things that will interfere with the normal soldering of the material. Brown soldering protects against many types of defects that can occur in work.

Specifications

There are two main grades of the substance, which are defined according to GOST as grade A and grade B:

Soldering of metals is carried out by first removing traces of oxides from their surface. Fluxes are used for this. They should prevent oxidation when heated and encourage good flow of molten solder.

For soldering copper products, borax solder ideally meets all requirements. The substance has been known since the Middle Ages. It was mined in the lakes of India and Tibet, then transported to Europe, where it was used for processing fabrics and leather, and producing glass.

Borax is widely used for working with metals. When manufacturing or repairing metal products, borax soldering is carried out. First of all, the method is used for parts made of copper and brass. A special type of this flux is used when repairing jewelry.

Toxicity[ | ]

The substance is low toxic for warm-blooded animals, LD50 for rats is 2.66 g/kg. Dust can irritate mucous membranes and adversely affect the respiratory system.

There is evidence that the substance reduces fertility. According to European Union (EU) regulations, substances and mixtures imported into the EU containing borax must be labeled with the warnings “May cause harm to fertility” and “May cause harm to the unborn child” from July 2015[5].

It is also indicated that long-term, over 10-15 years, consumption of borax in the form of food additives can provoke cancer[6].

Mole

All substances are made up of atoms and molecules. In chemistry, it is important to accurately measure the mass of substances that react and are produced as a result. By definition, the mole is the SI unit of quantity of a substance. One mole contains exactly 6.02214076×10²³ elementary particles. This value is numerically equal to Avogadro's constant NA when expressed in units of mol⁻¹ and is called Avogadro's number. Amount of substance (symbol n

) of a system is a measure of the number of structural elements. A structural element can be an atom, molecule, ion, electron, or any particle or group of particles.

Avogadro's constant NA = 6.02214076×10²³ mol⁻¹. Avogadro's number is 6.02214076×10²³.

In other words, a mole is an amount of substance equal in mass to the sum of the atomic masses of atoms and molecules of the substance, multiplied by Avogadro’s number. The unit of quantity of a substance, the mole, is one of the seven basic SI units and is symbolized by the mole. Since the name of the unit and its symbol are the same, it should be noted that the symbol is not declined, unlike the name of the unit, which can be declined according to the usual rules of the Russian language. One mole of pure carbon-12 is equal to exactly 12 g.

Notes[ | ]

1. ↑ 12
   https://www.cdc.gov/niosh/npg/npgd0057.html
2. ↑ 12345678910
   Fedorov, 1992.
3. Franz v Bruchhausen, Siegfried Ebel, Eberhard Hackenthal, Ulrike Holzgrabe.
   Hagers Handbuch der Pharmazeutischen Praxis: Folgeband 5: Stoffe LZ. - Springer-Verlag, 2013. - 299 p. — ISBN 978-3-642-58388-9.
4. ↑ 123
   Ioffis, 1981.
5. Recommendation of the European Chemicals Agency of 1 July 2015 for the inclusion of substances in Annex XIV to REACH (List of Substances subject to Authorisation) Echa.europa.eu. Retrieved on July 6, 2015.
6. Watch Out For The Food We Consume (undefined)
   . Directorate of Consumer Protection, Jakarta, Indonesia (2006). Access date: February 10, 2009. Archived December 28, 2008.

Content

• 1 Chemistry 1.1 Structure
• 1.2 Reactions

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• Levinson-Lessing F. Yu.
  Bura, being in nature // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg, 1890-1907.
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  Sodium borates // Chemical Encyclopedia: in 5 volumes / Ch. ed. I. L. Knunyants. - M.: Great Russian Encyclopedia, 1992. - T. 3: Copper-Polymer. — P. 180-181. — 639 p. — 48,000 copies. — ISBN 5-85270-039-8.

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