SODIUM CHLORIDE (NACL): STRUCTURE, PROPERTIES, USES - CHEMISTRY - 2025

The sodium chloride, also known as common salt or table salt, is a binary inorganic salt of the alkali metal sodium and chlorine halogen. It is the largest component of edible salt and its mineral form is known as halite. Its molecular formula is NaCl, and it describes the stoichiometric proportion of its ions (Na ⁺ Cl ^-) and not that of a discrete molecule (Na-Cl)

Sodium chloride is a white crystalline solid that is formed by the combination of sodium, a silvery-white metal, which reacts violently with water, and the element chlorine, a poisonous, corrosive and pale green gas.

Source: Pixabay

The upper image shows a portion of NaCl crystals. How is it possible that from two elements as dangerous as Na and Cl ₂, an edible salt can be formed? First, the chemical equation for its formation is:

2Na (s) + Cl ₂ (g) => 2NaCl (s)

The answer lies in the nature of the bond in NaCl. Being ionic, the properties of Na ⁺ and Cl ^- are diagonally different from those of their neutral atoms.

Sodium is a vital element, but in its ionic form. Na ⁺ is the main extracellular cation with a concentration of approximately 140 mEq / l, and together with its accompanying anions, Cl ^- and HCO ₃ ^- (bicarbonate), are the main responsible for the value of osmolarity and extracellular volume..

In addition, Na ⁺ is responsible for the generation and conduction of the nerve impulse in the neuronal axons, as well as for initiating muscle contraction.

NaCl has been used since ancient times to flavor food and to preserve meat, due to its ability to kill bacteria and prevent spoilage.

It is also necessary for the production of sodium hydroxide (NaOH) and molecular chlorine (Cl ₂), reacting NaCl with water under hydrolysis:

2H ₂ O (l) + 2 NaCl (s) => 2NaOH (aq) + Cl ₂ (g) + H ₂ (g)

H ₂ (g) and NaOH accumulate at the cathode (-). Meanwhile, Cl ₂ (g) accumulates at the anode (+). Sodium hydroxide is used in the manufacture of soaps and chlorine in the manufacture of PVC plastic.

Structure of sodium chloride

Source: By Solid State, from Wikimedia Commons

In the upper image the compact cubic structure of sodium chloride is represented. The voluminous green spheres correspond to Cl ^- anions, while the white ones to Na ⁺ cations. Note how the NaCl crystal consists of a network of ions arranged by their electrostatic interactions in a 1: 1 ratio.

Although bars are shown in the image, the bonds are not covalent but ionic. The use of bars is useful when showing coordination geometry around an ion. For example, in the case of NaCl each Na ⁺ is surrounded by six Cl ^- (octahedron of white color), and each Cl ^- of six Na ⁺ (octahedron of green color).

Therefore, it has a coordination (6,6) whose numbers indicate how many neighbors surround each ion. The number on the right indicates the neighbors of Na ⁺, while the one on the left, those of Cl ^-.

Other representations omit the use of bars to highlight the octahedral voids in the structure, which result from the interstitial space between six packed Cl ^- anions (or Na ⁺ cations). This arrangement is observed in other mono (MX) or polyatomic inorganic salts, and is called the gem salt.

Unit cell

The unit cell of rock salt is cubic, but which cubes exactly represent it in the image above? The octahedrons give the answer. Both cover a total cell made up of four small cubes.

These cubes have portions of the ions at their vertices, edges, and faces. Looking closely, one Na ⁺ ion is located in the center and twelve of them on the edges. An ion on an edge can be shared by four cubes. So there are 4 Na ⁺ ions (12 × 1/4 + 1 = 4).

For Cl ^- ions, eight are located at the vertices and six at the edges. As the ions positioned at the vertices share space with eight other cubes, and at the edges with six, we have 4 Cl ^- ions (8 × 1/8 + 6 × 1/2 = 4).

The above result is interpreted as follows: in the NaCl unit cell there are four Na ⁺ cations and four Cl ^- anions; proportion that agrees with the chemical formula (one Na ⁺ for each Cl ^-).

Properties

Molecular formula

NaCl.

Molecular weight

58.44 g / mol.

Physical description

A crystalline solid.

Color

Transparent colorless crystals or white crystalline powder.

Taste

Salty.

Boiling point

2,575 ° F at 760 mmHg.

1,465 ° C.

Melting point

1,474 ° F (800.7 ° C).

Both the boiling point and the melting point reflect the heat necessary to overcome the crystalline lattice energy. Therefore, these measurements confirm the ionic character of NaCl.

Water solubility

Greater than or equal to 100 mg / ml at 68ºF.

36.0 g / 100 ml at 25 ° C.

It is in fact a hygroscopic salt, which retains moisture from the environment.

Solubility in organic solvents

0.065 g / 100 mL of ethanol at 25 ° C; 10 g / 100 g of glycerol at 25 ° C; 2.15 g / 100 mL of liquid ammonia at 40 ° C; 1.4 g / 100 mL of methanol at 25 ° C; 7.15 g / 100 of ethylene glycol at 25 ° C and 5.21 g / 100 g of formic acid at 25 ° C.

Density

2.165 g / cm ³ at 77 ° C.

Vapor pressure

1 mmHg at 1,589ºF.

Stability

It is stable under recommended storage conditions.

Decomposition

When heated to high temperatures, it decomposes, emitting hydrochloric acid and disodium oxide vapors.

Viscosity

Viscosity of saturated solutions 1.93 mPa-s.

Corrosion

It is corrosive to many metals.

pH

6.7 to 7.3 in aqueous solution.

Applications

In food

-Sodium chloride has been used since ancient times to improve the taste of food and to preserve it. Salting meat is a way to preserve it from bacterial action, since it delays protein breakdown.

-On the other hand, salt increases the osmolarity around the meat, which causes the absorption by osmosis of the water of the bacteria, causing their elimination.

Industrial uses

Food industry

-In the food industry, salt is used as a flavor enhancer, fermentation control additive, texture control agent and color developer. For example, salt is added to bring out the color in bacon, ham, and other meat products.

-The salt serves as a binder in the manufacture of sausages. It contributes to the formation of a binder gel composed of meat, fat and moisture.

-In the processing of flour for bread making, salt is added during baking to control the rate of leavening of bread dough. It is also used to strengthen gluten and as a flavor enhancer, as well as a filling in baked goods.

-Used in the manufacture of breakfast cereals, mixed or prepared flours, potato chips, dog and cat food, etc.

Chemical synthesis

-Sodium chloride is used as a raw material in the production of sodium hydroxide and chlorine, which, in turn, are useful in many chemical industries.

-The salt is used in the processing of various metals, for example aluminum, copper, steel and vanadium. It is also used to make sodium chlorate, which is later used in the synthesis of chlorine dioxide, an oxygen-based bleach. Chlorine dioxide is less harmful to the environment than other bleaches.

In the leather industry

-The salt is used to inhibit the bacterial action inside the skins, as well as to help in their rehydration.

In the textile industry

-The salt is used as a mordant in the dyeing of fabrics. It is used as a brine rinse to remove organic contaminants and to create a positive charge on the surface of fabrics that allows negatively charged dyes to bind.

In the oil industry

-In oil and gas exploration, salt is an important component of well drilling fluids. It is used to flocculate and increase the density of drilling liquids, which allows to overcome the high gas pressures in the wells to be reached. In addition, the salt maintains the saturation of the drilling liquid.

-The salt helps to compact the soil on which the roads are built. Reduces the displacement caused in the subsoil by humidity changes and automotive traffic.

In the home

Salt has been used by rubbing in cleaning surfaces, pots and pans. Also in the prevention of mold and as a stain remover. It is also used in many brands of shampoo and toothpaste.

Other uses

On the roads

-In anticipation of snowfall, roads are covered with brine, which prevents the binding of ice to the road surface. For thawing, a mixture of brine and salt is used, and sometimes other chemical components such as magnesium or calcium chloride are added. The use of salt and brine is not effective at temperatures below -10 ºC.

Adding salt produces a decrease in the cryoscopic point, a colligative property of the solutions, thus hindering the formation of ice in a certain way.

-Because of its hygroscopic condition, salt is used as a cheap desiccant.

In resins used to soften water

Hard water contains calcium and magnesium ions that hinder the action of soap and cause deposits of alkaline materials on various equipment and pipes. In water softening, ion exchange resins are used. The salt is used in the preparation and regeneration of the resins.

In fire extinguishers

Sodium chloride is used in fire extinguishers to fight fires in which combustible metals are present, such as magnesium, potassium, sodium, and NK alloys.

Salt acts as a heat sink and also forms a crust that restricts oxygen access to the fire.

In the glasses

Sodium chloride crystals are used in optical components such as windows and prisms, especially for infrared light. However, since the salt is very hygroscopic, a kind of frost is produced that covers the lenses. For this reason, sodium chloride lenses have been replaced by zinc selenide (ZnSe) lenses.

Therapeutic uses

Supply the lack of salts in the body

-When there is a body depletion of Na ⁺, it must be replaced to maintain extracellular osmolarity, nerve conduction and muscle contraction.

-NaCl is used in the treatment and prevention of sodium and chlorine deficiency, resulting from excessive sweating during exposure to high temperatures. It is also used in an excessive diuresis or an excessive restriction of saline intake.

-Parenteral supply of a 045% NaCl solution is used in the management of hyperosmolar diabetes. It fulfills a rehydrating function and serves to assess the status of kidney function.

-Injections of hypertonic solutions, with a NaCl concentration greater than 0.9% w / v, -They are used when there is a severe depletion of Na ⁺, being a restoration of the essential ion. This hyponatremia can be the consequence of a treatment with free electrolytes or with a concentration of Na ⁺.

Hyponatremia can also be caused by excessive water intake, not controlled by inadequate kidney function.

In unconventional treatments and uses

-NaCl inhalation solutions are used to dilute the drugs used during the nebulization process. It is also used for tracheal lavage and irrigation. The 0.9% saline solution is used in nasal sprays.

-20% NaCl solutions are used for intra-amniotic transabdominal installation, thereby inducing a late abortion during the second trimester of pregnancy.

-Sodium chloride can be used as a local antiseptic. Thanks to its osmotic capacity, it is capable of dehydrating a wide spectrum of viruses and bacteria in a non-spurious state; therefore, it is used as a painful antiseptic to disinfect wounds.

Toxicity

Ingestion

It only has a harmful effect on health if the intake is high and for a long time. Under these circumstances, hypernatremia would occur with the consequent increase in extracellular volume that would lead to arterial hypertension.

Irritation and physical contact

It has a toxic effect only if the inhalation is very high. Excessive contact with the skin can cause it to be dry. Finally, it causes a momentary irritation on contact with the eyes.

References

1. Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition., Pp. 84, 90, 93, 263). Mc Graw Hill.
2. Whitten, Davis, Peck & Stanley. Chemistry. (8th ed.). CENGAGE Learning, p 482-483.
3. Sodium chloride. (2018). Sodium Chloride: Benefits, Uses, Properties, Risks. Taken from: sodium chloride.org
4. PubChem. (2018). Sodium Chloride. Recovered from: pubchem.ncbi.nlm.nih.gov
5. Wikipedia. (2018). Sodium chloride. Taken from: en.wikipedia.org
6. American Elements. (2018). Sodium Chloride. Taken from: americanelements.com