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What is barium carbonate?

The barium carbonate is an inorganic salt of the metal barium, penultimate element group 2 of the periodic table and belonging to alkaline earth metals. Its chemical formula is BaCO 3 and it is commercially available in the form of a white crystalline powder.

How is it obtained? Barium metal is found in minerals, such as barite (BaSO 4 ) and whiterite (BaCO 3 ). Whiterite is associated with other minerals that subtract levels of purity from their white crystals in exchange for colorations.

To generate BaCO 3 for synthetic use, it is necessary to remove impurities from whiterite, as indicated by the following reactions:

BaCO 3 (s, impure) + 2NH 4 Cl (s) + Q (heat) => BaCl 2 (aq) + 2NH 3 (g) + H 2 O (l) + CO 2 (g)

BaCl 2 (aq) + (NH 4 ) 2 CO 3 (s) => BaCO 3 (s) + 2NH 4 Cl (aq)

Barite, however, is the main source of barium, and that is why industrial productions of barium compounds are based on it. Barium sulfide (BaS) is synthesized from this mineral, a product from which the synthesis of other compounds and BaCO 3 result :

BaS (s) + Na 2 CO 3 (s) => BaCO 3 (s) + Na 2 S (s)

BaS (s) + CO 2 (g) + H 2 O (l) => BaCO 3 (s) + (NH 4 ) 2 S (aq)

Barium carbonate properties

Barium carbonate powder

It is a white, crystalline, powdery solid. It is odorless, tasteless, and its molecular weight is 197.89 g / mol. It has a density of 4.43 g / mL and a non-existent vapor pressure.

It has refractive indices of 1,529, 1,676, and 1,677. Witherite emits light when it absorbs ultraviolet radiation: from bright white light with bluish hues, to yellow light.

It is highly insoluble in water (0.02 g / L) and in ethanol. In acid solutions of HCl, it forms the soluble salt of barium chloride (BaCl 2 ), which explains its solubility in these acidic media. In the case of sulfuric acid, it precipitates as the insoluble salt BaSO 4 .

BaCO 3 (s) + 2HCl (aq) => BaCl 2 (aq) + CO 2 (g) + H 2 O (l)

BaCO 3 (s) + H 2 SO 4 (aq) => BaSO 4 (s) + CO 2 (g) + H 2 O (l)

As it is an ionic solid, it is also insoluble in nonpolar solvents. Barium carbonate melts at 811 ° C; if the temperature rises around 1380-1400 ºC, the salty liquid undergoes chemical decomposition instead of boiling. This process occurs for all metallic carbonates: MCO 3 (s) => MO (s) + CO 2 (g).

Thermal decomposition

BaCO 3 (s) => BaO (s) + CO 2 (g)

If ionic solids are characterized by being very stable, why do carbonates decompose? Does the metal M change the temperature at which the solid decomposes? The ions that make up barium carbonate are Ba 2+ and CO 2– , both bulky (that is, with large ionic radii). CO 2– is responsible for decomposition:

The oxide ion (O 2– ) binds to the metal to form MO, the metal oxide. MO generates a new ionic structure in which, as a general rule, the more similar the size of its ions, the more stable the resulting structure (lattice enthalpy). The opposite occurs if the M + and O 2– ions have very unequal ionic radii.

If the lattice enthalpy for MO is large, the decomposition reaction is energetically favored, requiring lower heating temperatures ( lower boiling points ).

On the other hand, if MO has a small lattice enthalpy (as in the case of BaO, where Ba 2+ has a higher ionic radius than O 2– ) decomposition is less favored and requires higher temperatures (1380-1400ºC). In the cases of MgCO 3 , CaCO 3  and SrCO 3 , they decompose at lower temperatures.

Chemical structure

Barium carbonate

The CO 2– anion has a double bond resonating between three oxygen atoms, two of which are negatively charged to attract the Ba 2+ cation .

Although both ions can be considered charged spheres, CO 2– has a trigonal plane geometry (the flat triangle drawn by the three oxygen atoms), possibly becoming a negative “pad” for Ba 2+ .

These ions interact electrostatically to form a crystalline arrangement of the orthorhombic type, the bonds being predominantly ionic.

In that case, why is BaCO 3 not soluble in water? The explanation is based simply on the fact that the ions are better stabilized in the crystal lattice than hydrated by spherical molecular layers of water.

From another angle, water molecules have a hard time overcoming the strong electrostatic attractions between the two ions. Within these crystal lattices they can harbor impurities that give their white crystals their color.

Applications

At first glance, a portion of BaCO 3  may not promise any practical application in daily life, but if you look at a crystal of the mineral whiterite, white as milk, the reason for its economic demand begins to make sense.

It is used to make barium glasses or as an additive to strengthen them. It is also used in the manufacture of optical glasses.

Due to its great network enthalpy and insolubility, it is used in the manufacture of different types of alloys, rubbers, valves, floor coverings, paints, ceramics, lubricants, plastics, greases and cements.

It is also used as a mouse poison. In synthesis, this salt is used to produce other barium compounds, and thus serve as materials for electronic devices.

BaCO 3 can be synthesized as nanoparticles, expressing new interesting properties of whiterite on very small scales. These nanoparticles are used to impregnate metal surfaces, specifically chemical catalysts.

It has been found that it improves oxidation catalysts, and that it somehow favors the migration of oxygen molecules across their surface.

They are considered as implements to accelerate the processes in which oxygen is incorporated. And finally, they are used to synthesize supramolecular materials.

Risks

BaCO 3 is poisonous if swallowed, causing a myriad of unpleasant symptoms that lead to death from respiratory failure or cardiac arrest; for this reason it is not recommended to be transported together with edible goods.

It causes redness of the eyes and skin, as well as a cough and a sore throat. It is a toxic compound, although easily manipulated with bare hands if ingestion is avoided at all costs.

It is not flammable, but at high temperatures it decomposes forming BaO and CO 2 , toxic and oxidizing products that can ignite other materials.

In the body, barium is deposited in bones and other tissues, supplanting calcium in many physiological processes. It also blocks the channels through which K + ions travel , preventing their diffusion through cell membranes.

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