- Structure
- Crystal lattice energy
- Hydrates
- Preparation or synthesis
- Properties
- Physical appearance
- Molecular mass
- Density
- Melting point
- Boiling point
- Water solubility
- Thermal decomposition
- Nomenclature
- Applications
- Oxygen producer
- Hydrogen peroxide producer
- References
The barium peroxide is an ionic and inorganic compound whose chemical formula is BaO 2. Being an ionic compound, it consists of Ba 2+ and O 2 2- ions; The latter is what is known as the peroxide anion, and because of it BaO 2 acquires its name. Thus, BaO 2 is an inorganic peroxide.
The charges of its ions reveal how this compound is formed from the elements. The barium metal, of group 2, gives two electrons to the oxygen molecule, O 2, whose atoms do not use them to reduce themselves to the oxide anions, O 2-, but to remain united by a simple bond, 2-.
BaO2 solid. Source: Ondřej Mangl, from Wikimedia Commons
Barium peroxide is a granular solid at room temperature, white in color with slight grayish tones (upper image). Like almost all peroxides, it must be handled and stored with care, as it can accelerate the oxidation of certain substances.
Of all the peroxides formed by the metals of group 2 (Mr. Becambara), BaO 2 is thermodynamically the most stable against its thermal decomposition. When heated, it releases oxygen and barium oxide, BaO, is produced. BaO can react with oxygen in the environment, at high pressures, to form BaO 2 again.
Structure
Crystal structure of BaO2. Source: Orci, via Wikimedia Commons
The upper image shows the tetragonal unit cell of barium peroxide. Inside it you can see the Ba 2+ cations (white spheres), and the O 2 2- anions (red spheres). Notice that the red spheres are joined by a single bond, so they represent linear geometry 2-.
From this unit cell, BaO 2 crystals can be built. If it is observed, the anion O 2 2- it is seen that it is surrounded by six Ba 2+, obtaining an octahedron whose vertices are white.
On the other hand, even more evident, each Ba 2+ is surrounded by ten O 2 2- (white sphere in the center). All crystal consists of this constant short and long range order.
Crystal lattice energy
If the red white spheres are also observed, it will be noted that they do not differ too much in their sizes or ionic radii. This is because the Ba 2+ cation is very bulky, and its interactions with the O 2 2- anion stabilize the lattice energy of the crystal to a better degree compared to how, for example, Ca 2+ and Mg cations would. 2+.
This also explains why BaO is the most unstable of the alkaline earth oxides: the Ba 2+ and O 2- ions differ considerably in size, destabilizing their crystals.
As it is more unstable, the lower the tendency for BaO 2 to decompose to form BaO; Unlike the peroxides SrO 2, CaO 2 and MgO 2, whose oxides are more stable.
Hydrates
BaO 2 can be found in the form of hydrates, of which BaO 2 ∙ 8H 2 O is the most stable of all; and in fact, this is the one that is marketed, instead of the anhydrous barium peroxide. To obtain the anhydrous one, BaO 2 ∙ 8H 2 O must be dried at 350 ° C, in order to eliminate the water.
Its crystalline structure is also tetragonal, but with eight H 2 O molecules interacting with O 2 2- through hydrogen bonds, and with Ba 2+ through dipole-ion interactions.
Other hydrates, whose structures there is not much information in this regard, are: BaO 2 ∙ 10H 2 O, BaO 2 ∙ 7H 2 O and BaO 2 ∙ H 2 O.
Preparation or synthesis
The direct preparation of barium peroxide consists of the oxidation of its oxide. This can be used from the mineral barite, or from the barium nitrate salt, Ba (NO 3) 2; both are heated in an air or oxygen-enriched atmosphere.
Another method consists of reacting Ba (NO 3) 2 with sodium peroxide in a cold aqueous medium:
Ba (NO 3) 2 + Na 2 O 2 + xH 2 O => BaO 2 ∙ xH 2 O + 2NaNO 3
Then the BaO 2 * xH 2 O hydrate is heated, filtered and dried using vacuum.
Properties
Physical appearance
It is a white solid that can turn greyish if it contains impurities (either BaO, Ba (OH) 2, or other chemical species). If it is heated to a very high temperature, it will give off greenish flames, due to the electronic transitions of the Ba 2+ cations.
Molecular mass
169.33 g / mol.
Density
5.68 g / mL.
Melting point
450 ° C.
Boiling point
800 ° C. This value is consistent with what should be expected of an ionic compound; and even more, the most stable alkaline earth peroxide. However, BaO 2 does not actually boil, but gaseous oxygen is released as a result of its thermal decomposition.
Water solubility
Insoluble. However, it can slowly undergo hydrolysis to produce hydrogen peroxide, H 2 O 2; and furthermore, its solubility in aqueous medium increases if a dilute acid is added.
Thermal decomposition
The following chemical equation shows the thermal decomposition reaction that BaO 2 undergoes:
2BaO 2 <=> 2BaO + O 2
The reaction is one-way if the temperature is above 800 ° C. If the pressure is immediately increased and the temperature decreases, all the BaO will be transformed back into BaO 2.
Nomenclature
Another way to name BaO 2 is barium peroxide, according to the traditional nomenclature; since barium can only have the valence +2 in its compounds.
Wrongly, the systematic nomenclature is used to refer to it as barium dioxide (binoxide), considering it an oxide and not a peroxide.
Applications
Oxygen producer
Using the mineral barite (BaO), it is heated with currents of air to eliminate its oxygen content, at a temperature of around 700 ° C.
If the resulting peroxide is gently heated under vacuum, the oxygen is regenerated more quickly and the barite can be reused indefinitely to store and produce oxygen.
This process was commercially devised by LD Brin, now obsolete.
Hydrogen peroxide producer
Barium peroxide reacts with sulfuric acid to produce hydrogen peroxide:
BaO 2 + H 2 SO 4 => H 2 O 2 + BaSO 4
It is therefore a source of H 2 O 2, manipulated above all with its hydrate BaO 2 ∙ 8H 2 O.
According to these two uses mentioned, BaO 2 allows the development of O 2 and H 2 O 2, both oxidizing agents, in organic syntheses and in bleaching processes in the textile and dye industries. It is also a good disinfecting agent.
In addition, other peroxides can be synthesized from BaO 2, such as sodium, Na 2 O 2, and other barium salts.
References
- SC Abrahams, J Kalnajs. (1954). The crystal structure of barium peroxide. Laboratory for Insulation Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Wikipedia. (2018). Barium peroxide. Recovered from: en.wikipedia.org
- Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
- Atomistry. (2012). Barium peroxide. Recovered from: barium.atomistry.com
- Khokhar et al. (2011). Study of Laboratory Scale Preparation and Development of a Process for Barium Peroxide. Recovered from: academia.edu
- PubChem. (2019). Barium peroxide. Recovered from: pubchem.ncbi.nlm.nih.gov
- PrebChem. (2016). Preparation of barium peroxide. Recovered from: prepchem.com