Chemical elements
    Physical Properties
    Chemical Properties
      Bismuth Trihydride
      Bismuth Trifluoride
      Bismuthyl Fluoride
      Bismuth Trichloride
      Bismuth Oxychloride
      Bismuth Chlorate
      Bismuthyl Perchlorates
      Bismuth Thiochloride
      Bismuth Selenochloride
      Bismuth Dibromide
      Bismuth Tribromide
      Bismuth Oxybromide
      Bismuth Thiobromide
      Bismuth Diiodide
      Bismuth Triiodide
      Bismuth Oxyiodide
      Bismuth Iodate
      Bismuth Thioiodide
      Bismuth Monoxide
      Bismuth Trioxide
      Bismuth Hydroxide
      Bismuth Tetroxide
      Bismuth Pentoxide
      Bismuth Hexoxide
      Bismuth Monosulphide
      Bismuth Trisulphide
      Bismuth Sulphites
      Bismuth Sulphate
      Bismuth Thiosulphates
      Bismuth Triselenide
      Bismuth Chromite
      Bismuth Nitride
      Bismuthyl Nitrite
      Normal Bismuth Nitrate
      Basic Bismuth Nitrate
      Bismuth Phosphide
      Bismuth Hypophosphite
      Bismuth Phosphite
      Bismuth Orthophosphate
      Bismuth Pyrophosphate
      Bismuth Thiophosphate
      Bismuth Arsenide
      Bismuth Arsenite
      Bismuth Arsenate
      Bismuth Carbonate
      Bismuth Cyanides
      Bismuth Thiocyanate
      Bismuth Chromothiocyanate
      Bismuth Orthosilicate
    Detection and Estimation

Bismuth Tetroxide, Bi2O4

Bismuth Tetroxide, Bi2O4, hydrated with one or two molecules of water, is formed when sodium bismuthate is decomposed with nitric acid; the anhydrous substance has not been obtained by this method, as oxygen is lost when water is removed.

Four different modifications have been obtained by the action of various oxidising agents upon a suspension of bismuth trioxide in boiling solutions of dilute alkali hydroxides. Two of these modifications are anhydrous, the others being modifications of the monohydrate, Bi2O4.H2O. A dihydrated Bi2O4.2H2O, is obtained by the action of chlorine upon a suspension of trioxide in a boiling, concentrated solution of alkali hydroxide; it is always contaminated with a hydrated pentoxide, from which it can be separated by treatment with boiling, concentrated nitric acid.

Anhydrous bismuth tetroxide is brown or purplish-black. Its density (at 20° C.) is 5.60 to 5.75, that of the dihydrate being 5.80. The anhydrous substance is stable at 100° C., but loses oxygen at 160° C. The monohydrates begin to lose water at 100° C., and are decomposed at 160° C., whilst the dihydrate is decomposed at 100° C., losing both oxygen and water. The tetroxide is not attacked by dilute nitric or sulphuric acid. The crude substance as usually prepared is partially dissolved by more concentrated nitric acid (density 1.2) at 70° to 90° C., with evolution of oxygen, the insoluble residue having a composition corresponding to that of bismuth tetroxide. From this it is deduced that the usual preparations are mixtures, probably of tetroxide and pentoxide. The tetroxide reacts with concentrated oxygen acids to form tervalent bismuth salts with evolution of oxygen. It is very sparingly soluble in alkali hydroxide.

Bismuth tetroxide can be reduced by hydrogen and by carbon monoxide. Hydrogen peroxide is decomposed by it. It is a powerful oxidising agent; hydrochloric acid is oxidised to chlorine even at -15° C., and manganous salts are oxidised to permanganate immediately in the cold in the presence of nitric acid.

With hydrochloric acid there is no indication of the formation of a chloride of quadrivalent bismuth.

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