Chemical elements
    Physical Properties
    Chemical Properties
      Barium Hydride
      Barium Subfluoride
      Barium Fluoride
      Acid Barium Fluoride
      Barium Subchloride
      Barium Chloride
      Barium Bromide
      Barium Perbromides
      Barium Iodide
      Barium Periodides
      Barium Mixed Halides
      Barium Mixed Perhalides
      Barium Oxychloride
      Barium Hypochlorite
      Barium Chlorite
      Barium Chlorate
      Barium Perchlorate
      Barium Oxybromide
      Barium Hypobromite
      Barium Bromate
      Barium Perbromate
      Barium Oxyiodide
      Barium Iodate
      Barium Periodate
      Barium Manganites
      Barium Manganate
      Barium Permanganate
      Barium Suboxide
      Barium Oxide
      Barium Hydroxide
      Barium Peroxide
      Barium Peroxyhydrate
      Barium Tetroxide
      Barium Sulphide
      Barium Hydrosulphide
      Barium Polysulphides
      Barium Hydroxyhydrosulphide
      Barium Oxysulphides
      Barium Sulphite
      Barium Thiosulphate
      Barium Dithionate
      Barium Trithionate
      Barium Tetrathionate
      Barium Pentathionate
      Barium Sulphate
      Acid Barium Sulphates
      Barium Pyrosulphate
      Barium Persulphate
      Barium Selenide
      Barium Selenite
      Barium Selenate
      Acid Barium Selenate
      Barium Telluride
      Barium Tellurite
      Barium Tellurate
      Barium Chromite
      Barium Chromate
      Barium Dichromate
      Barium Potassium Trichromate
      Barium Chlorochromate
      Barium Perchromate
      Barium Molybdate
      Barium Permolybdate
      Barium Tungstate
      Barium Uranate
      Barium Diuranate
      Barium Peruranate
      Barium Nitride
      Barium Azide
      Barium Hexammoniate
      Barium Ammonium
      Barium Amide
      Barium Amidosulphonate
      Barium Imide
      Barium Imidosulphonate
      Barium Hyponitrite
      Barium Nitroxysulphite
      Barium Nitrososulphate
      Barium Nitrohydroxylaminate
      Barium Nitrite
      Barium Nitrate
      Barium Phosphide
      Barium Dihydrohypophosphite
      Barium Hydrophosphite
      Barium Hypophosphate
      Barium Orthophosphates
      Barium Pyrophosphate
      Barium Metaphosphate
      Basic Barium Phosphates
      Barium Thiophosphites
      Barium Thiophosphates
      Barium Selenophosphates
      Barium Azophosphates
      Barium Phosphimates
      Barium Arsenide
      Barium Orthoarsenite
      Barium Pyroarsenite
      Barium Orthoarsenates
      Barium Pyroarsenate
      Barium Thioarsenites
      Barium Thioarsenates
      Barium Sodium Selenoxyarsenate
      Barium Metantimonate
      Barium Thioantimonites
      Barium Chloroantimonite
      Barium Orthothioantimonate
      Barium Hypovanadate
      Barium Vanadates
      Barium Metapervanadate
      Barium Niobate
      Barium Tantalate
      Barium Pertantalate
      Barium Carbide
      Barium Carbonyl
      Barium Formate
      Barium Acetate
      Barium Oxalate
      Barium Carbonate
      Barium Thiocarbonate
      Barium Percarbonate
      Barium Cyanide
      Barium Cyanamide
      Barium Cyanate
      Barium Cyanurate
      Barium Thiocyanate
      Barium Selenocyanate
      Barium Silicide
      Barium Silicates
      Barium Fluosilicate
      Barium Stannate
      Barium Orthoplumbate
      Barium Titanate
      Barium Peroxide Pertitanate
      Barium Pertitanate
      Barium Fluoroxytitanate
      Barium Zirconate
      Barium Boride
      Barium Borates
      Barium Fluorborate
      Barium Perborate
      Barium Aluminates
      Barium Ferrite
      Barium Ferrate
      Barium Gobaltite
      Barium Dinickelite
      Barium Platinate
    Detection of Barrium
    PDB 1djh-3iqp
    PDB 3iqr-4e7y

Barium Peroxide, BaO2

Thenard observed that barium oxide absorbs oxygen probably equal in amount to that which is already present, and forms a Barium Peroxide, BaO2. The rate of reaction is practically zero at ordinary temperatures, but reaches an appreciable velocity above 400° C. At the same time, however, since combination with oxygen is accompanied by an evolution of 12.1 Cal. per gram-molecule, the tendency to dissociate again into barium oxide and oxygen is increased, and an increased pressure of oxygen is, therefore, necessary to bring about complete transformation into peroxide. Thus, by heating the oxide alternately at a lower temperature, and then at a higher one, in air, it was found possible to use it as a means of separating oxygen from the air. It was observed that the reactants must not be absolutely anhydrous, but that at the same time the amount of water present must be small. The process was modified by Brin, who kept the temperature constant and alternately raised and lowered the pressure. The air had to be previously purified from carbon dioxide and organic matter, and a porous oxide was necessary. Brin's process for obtaining oxygen has now been superseded by air-fraetionation methods.

Recent work on the catalytic acceleration of the reaction by various oxides, for example copper, zinc, cadmium, magnesium, calcium, silicon, antimony, bismuth, uranium, tungsten, and molybdenum oxides, has suggested the possible revival of the Brin process under more favourable conditions of temperature. Some of the oxides mentioned form stable salts with barium, and would, therefore, be unsuitable for commercial purposes, as they would no doubt soon put the barium oxide out of action.

Barium peroxide is a white powder, stable under ordinary conditions if anhydrous, and protected from carbon dioxide. It melts at bright red heat with the evolution of oxygen. When heated with hydrogen, water, sulphur, carbon, carbon monoxide, sulphur dioxide, or ammonia, it is reduced. By heating with chlorine, or iodine, the oxygen is replaced by the halogerf. With concentrated sulphuric acid at ordinary temperatures ozonised oxygen is given off. With dilute hydrochloric acid, hydrogen peroxide is formed, and oxygen with concentrated. Potassium ferricyanide is reduced by barium peroxide, forming a double potassium barium ferrocyanide and free oxygen, and this reaction may be used as a means of estimating barium peroxide. With formaldehyde, barium formate and hydrogen are produced. By heating to redness with precipitated metallic gold a bright green mass is obtained which, on treatment with water, gives a solution of barium aurate, Ba(AuO2)2.

The dissociation pressures of barium peroxide for different temperatures were first investigated by Le Chatelier. The difficulty of the determinations is much enhanced by the fact that a solid solution of barium oxide and peroxide is formed, so that the pressure at any one temperature will be influenced by the proportions of these two present, and, further, by the necessity for the presence of water vapour. The dissociation has, however, been carefully studied by Hildebrand. As already stated, a small amount of water is necessary as a catalyst. After some of the peroxide has been decomposed, barium hydroxide will therefore be present. Experiments on the vapour pressure of barium hydroxide do not indicate the formation of a solid solution with the oxide, and the same is probably true of the peroxide and hydroxide.

Starting from the peroxide, the system is at first divariant. There are three components, water, barium oxide, and oxygen; and three phases, barium hydroxide, an unsaturated solid solution of barium oxide in barium peroxide, and the gaseous phase composed of oxygen and water vapour. Therefore there are two degrees of freedom. At any one temperature the oxygen pressure will vary with the concentration of the solid solution, which will depend on the proportion of barium peroxide decomposed. When about one-third of the peroxide has been decomposed the barium peroxide is saturated with barium oxide, and the system become monovariant owing to the appearance of a second solid solution of the two, thus making a fourth phase. The composition of the two saturated solid solutions may vary slightly with varying temperature, but at constant temperature will remain constant, although the amount of the second solution will increase at the expense of the first as the proportion of barium peroxide is diminished. The point at which the system becomes monovariant depends on the amount of water present, and hence on the amount of barium hydroxide which will be formed. The system again becomes divariant when about 98 per cent, of the peroxide has been decomposed.

The conditions necessary to produce 100 per cent, barium peroxide from barium oxide were studied. Oxygen of definite moisture content, which was less than the vapour pressure of barium hydroxide at the temperature under consideration, was passed, under slightly more than one atmosphere pressure, over barium oxide heated to a definite temperature in an electric oven. Successive equal samples were acted upon for equal times and the product analysed. Similar experiments were carried out with air. The following results were obtained: -

Temperature, °C200300350400500600700750800900
Percentage BaO2, using oxygen.3.717.371.196.410010096.961.918.20.9
Percentage BaO2, using air.18.270.469.252.830.95.9

With sufficient water present to give the vapour pressure of barium hydroxide, and sufficient barium oxide to produce the monovariant system, the following values for the pressure were obtained and compared with the values calculated from the equation

log10p = -6850/T + 1.75 log10T + 3.807, where T is the absolute temperature and p is expressed in mm.

These are all lower than Le Chatelier's values. The heat of combination of barium oxide and oxygen calculated from these results is 18.71 Cal. per gram-molecule of peroxide. The disagreement with Berthelot's value, 12.1 Cal., seems too large to be accounted for by the formation of solid solutions.

Hydrates of Barium Peroxide

Anhydrous barium peroxide combines with water with the evolution of 9.1 Cal. of heat per gram-molecule. The octahydrate, BaO2.8H2O, in pearly plates, is formed, but the formula BaO2.10H2O and 7H2O have also been assigned to it.

When barium peroxide is obtained by precipitation of barium hydroxide solution with hydrogen peroxide, the octahydrate is always formed at ordinary temperatures if less than one molecule of hydrogen peroxide be present per molecule of hydroxide, and above 60° C. whatever the composition of the solution. Jaubert patented a process for obtaining hydrated barium peroxide by lixiviating barium sulphide with boiling water, cooling to 25°-30° C., and adding sodium peroxide in cold water. The barium peroxide separates out in scales which may be filtered, washed, and pressed.

The octahydrate effloresces on exposure to air, and carbonate is also formed.

Berthelot mentions a monohydrate, heat of hydration 1.4 Cal., but it is probably the peroxyhydrate.

Barium peroxide may be estimated iodometrically by adding potassium iodide to a hydrochloric acid solution of the compound and titrating the liberated iodine with thiosulphate, or by titrating with permanganate a hydrochloric acid solution to which a considerable quantity of manganous sulphate solution has afterwards been added. A sulphuric acid solution cannot be employed, because the precipitated sulphate carries with it a large quantity of peroxide which escapes reaction.

Barium peroxide may be used for bleaching purposes, but its chief use is in the production of hydrogen peroxide by decomposition with an acid.
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