RiesgosThe 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 therefore the 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)
Physical and chemical properties
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)
Since 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 3 2–, both bulky (that is, with large ionic radii). CO 3 2– is responsible for decomposition:
CO 3 2– (s) => O 2– (g) + CO 2 (g)
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–) the 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
Original text
Riesgos
El BaCO3 es venenoso por ingestión, causando una infinidad de síntomas desagradables que conducen a la muerte por insuficiencia respiratoria o paro cardíaco; por este motivo no se recomienda ser transportado junto a bienes comestibles.
Produce enrojecimiento de los ojos y de la piel, además de tos y dolor de garganta. Es un compuesto tóxico, aunque fácilmente manipulable con las manos desnudas si se evita a toda costa su ingestión.
No es inflamable, pero a altas temperaturas se descompone formando BaO y CO2, productos tóxicos y oxidantes que pueden hacer arder otros materiales.
En el organismo el bario se deposita en los huesos y otros tejidos, suplantando al calcio en muchos procesos fisiológicos. También bloquea los canales por donde viaja los iones K+, impidiendo su difusión a través de las membranas celulares.
Referencias
- PubChem. (2018). Barium Carbonate. Recuperado el 24 de marzo de 2018, de PubChem: pubchem.ncbi.nlm.nih.gov
- Wikipedia. (2017). Barium carbonate. Recuperado el 24 de marzo de 2018, de Wikipedia: en.wikipedia.org
- ChemicalBook. (2017). Barium carbonate. Recuperado el 24 de marzo de 2018, de ChemicalBook: chemicalbook.com
- Hong T., S. Brinkman K., Xia C. (2016). Barium Carbonate Nanoparticles as Synergistic Catalysts for the Oxygen Reduction Reaction on La0.6Sr0.4Co0.2Fe0.8O3!d Solid-Oxide Fuel Cell Cathodes. ChemElectroChem 3, 1 – 10.
- Robbins Manuel A. (1983).Robbins The Collector’s Book of Fluorescent Minerals. Fluorescent minerals description, p-117.
- Shiver & Atkins. (2008). Química Inorgánica. En La estructura de los sólidos simples (cuarta edición., pág. 99-102). Mc Graw Hill.