Chemical elements
    Physical properties
    Chemical properties
      Boron Hydrides
      Boron trihydride
      Boron halogen
      Boron trifluoride
      Hydrofluoboric acid
      Potassium borofluoride
      Fluoboric acid
      Perfluoboric acid
      Boron subchloride
      Boron trichloride
      Boron tribromide
      Boron tri-iodide
      Oxides of Boron
      Tetraboron trioxide
      Boron dioxide
      Tetraboron pentoxide
      Boron sesqui-oxide
      Boron trioxide
      Boric anhydride
      Boric Acids
      Orthoboric acid
      Boric acid
      Boracic acid
      Complex Boric Acids
      Perboric Acid and Perborates
      Sodium perborate
      Sodium hyperborate
      Potassium perborate
      Rubidium perborate
      Ammonium perborate
      Barium perborate
      Boron sesquisulphide
      Boron trisulphide
      Boron pentasulphide
      Boron selenide
      Boron nitride
      Boron amide
      Boron imide
      Boron phosphide
      Boron phospho-iodides
      Boron carbide
      Boron thiocyanate
      Boron Alkyls
      Boron trimethyl
      Boron Silicides and

Sodium perborate, NaBO3

Sodium perborate, NaBO3.4H2O, may be prepared by adding to a saturated solution of borax an equivalent quantity of sodium hydroxide and twice the amount of hydrogen peroxide theoretically necessary; after some time the perborate commences to crystallise out: -

Na2B4O7 + 2NaOH + 4H2O2 = 4NaBO3 + 5H2O.

In preparing the salt on a large scale the necessary ingredients are mixed in small batches, which are then united and slowly cooled with stirring. Wooden vats and stirrers are used, and metal pipes, etc., well tinned to minimise decomposition of the hydrogen peroxide. The temperature after mixing is 25°, and the concentrations are chosen so that the perborate separates out slowly. Large and fairly stable crystals are deposited, which are centri- fuged free from mother liquor and dried in a stream of pure air at a temperature not exceeding 50° C.

Sodium perborate is only formed in minute quantities at the anode when aqueous sodium orthoborate, with or without excess of alkali, is electrolysed. Sodium perborate, NaBO3.4H2O, crystallises in large, transparent, monoclinic prisms, and is stable in air free from carbon dioxide. The monohydrate may be obtained by careful drying, and this may be completely dehydrated in vacuo over phosphoric anhydride. The solubility of the salt in water, in grams per litre of solution, is as follows: -

Temp. °C15°21°26°32°
Grams of NaBO.4H2025.526.928.537.8

The solubility is augmented by the addition of boric, tartaric, or citric acid, glycerol, or ammonium and magnesium sulphates in small amount. The heat of solution in water is -11.56 Cals. at 16°; in seminormal sulphuric acid it is -8.95 Cals. at 17° C.

In aqueous solution at 0° C. the hydrolysis of sodium perborate is very slight, and from conductivity measurements it follows that the molecular formula of the salt is NaBO3. With rise of temperature, hydrolysis proceeds further, and at 25° it is very considerable. The aqueous solution has an alkaline reaction. According to Pissarjewsky, the hydrolysis proceeds in two stages, (i.) and (ii.), the third reaction (iii.) then taking place between products formed in (i.) and (ii.): -

(i.) NaBO3 + 2H2ONaO.OH + H3BO3
(ii.) NaO.OH + H2ONaOH + H2O2
(iii.) 3NaOH + H3BO3Na3BO3 + 3H2O

When heated above 40°, sodium perborate solution commences to evolve oxygen. The solution is an energetic oxidiser, converting ferrous salts to ferric, chromic salts to chromic acid, manganous salts to manganese dioxide, liberating chlorine from hydrochloric acid, iodine from potassium iodide, etc. Sodium perborate is used commercially under the name of " perborin " for bleaching purposes, since it may be incorporated into soaps and washing-powders. " Perborin M" contains soap, alkali, and sodium perborate; " persil " contains soap, alkali carbonate and silicate, and sodium perborate; "ozonite" is similar to " persiland "clarax" contains borax, sodium phosphate, and sodium perborate.

A sodium perborate of the composition NaB2O4.5H2O is said by Jaubert to be obtained when an intimate mixture of 248 grams of boric acid and 78 grams of sodium peroxide is slowly added to 2 litres of cold water. It cannot be recrystallised from water.

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