Chemical elements
  Sodium
    Isotopes
    Energy
    Preparation
    Applications
    Physical Properties
    Chemical Properties
      Sodium hydride
      Sodium fluoride
      Sodium hydrogen fluoride
      Sodium chloride
      Sodium bromide
      Sodium iodide
      Sodium hypochlorite
      Sodium chlorate
      Sodium hypobromite
      Sodium bromate
      Sodium hypoiodite
      Sodium iodate
      Sodium periodates
      Sodium monoxide
      Sodium peroxide
      Sodium hydroxide
      Sodium perhydroxide
      Sodium monosulphide
      Sodium polysulphides
      Sodium hydrogen sulphide
      Sodium sulphite
      Sodium hydrogen sulphite
      Sodium potassium sulphite
      Sodium pyrosulphite
      Sodium sulphate
      Sodium hydrogen sulphate
      Sodium monopersulphate
      Sodium pyrosulphate
      Sodium persulphate
      Sodium thiosulphate
      Sodium dithionate
      Sodium trithionate
      Sodium tetrathionate
      Sodium pentathionate
      Sodium hyposulphite
      Sodium selenides
      Sodium selenite
      Sodium selenate
      Sodium sulphodiselenide
      Sodium tellurides
      Sodium tellurate
      Sodium nitride
      Sodium hydrazoate
      Sodamide
      Sodium hydrazide
      Sodium hyponitrite
      Sodium nitrite
      Disodium nitrite
      Sodium nitrate
      Sodium phosphides
      Sodium dihydrophosphide
      Sodium hypophosphite
      Sodium phosphites
      Sodium dihydrogen phosphite
      Sodium hypophosphates
      Sodium orthophosphates
      Disodium hydrogen orthophosphate
      Sodium pyrophosphate
      Disodium dihydrogen pyrophosphate
      Sodium metaphosphate
      Sodium polyphosphate
      Sodium arsenites
      Sodium arsenates
      Sodium antimonate
      Sodium carbide
      Sodium carbonate
      Sodium hydrogen carbonate
      Sodium percarbonate
      Sodium cyanide
      Sodium thiocyanate
      Sodium silicates
      Sodium borates
    PDB 131d-1bli
    PDB 1bph-1d10
    PDB 1d11-1ej2
    PDB 1eja-1gb5
    PDB 1gb6-1goh
    PDB 1gq2-1ikp
    PDB 1ikq-1jz1
    PDB 1jz2-1kvs
    PDB 1kvt-1me8
    PDB 1mg2-1nsz
    PDB 1nta-1oyt
    PDB 1p0s-1qjs
    PDB 1qnj-1s5d
    PDB 1s5e-1tjp
    PDB 1tk6-1uxt
    PDB 1uxu-1vzq
    PDB 1w15-1xc6
    PDB 1xcu-1yf1
    PDB 1ygg-1zko
    PDB 1zkp-2afh
    PDB 2agv-2bhc
    PDB 2bhp-2cc6
    PDB 2cc7-2dec
    PDB 2deg-2ein
    PDB 2eit-2fjb
    PDB 2fld-2gg8
    PDB 2gg9-2h9j
    PDB 2h9k-2ien
    PDB 2ieo-2jih
    PDB 2jin-2omd
    PDB 2omg-2p77
    PDB 2p78-2q68
    PDB 2q69-2qz7
    PDB 2qzi-2v35
    PDB 2v3h-2vwo
    PDB 2vx4-2wig
    PDB 2wij-2x1z
    PDB 2x20-2xmk
    PDB 2xmm-2zfq
    PDB 2zfr-3a6s
    PDB 3a6t-3b1e
    PDB 3b2n-3bos
    PDB 3bov-3ccr
    PDB 3ccs-3d7r
    PDB 3d97-3e3y
    PDB 3e40-3erp
    PDB 3euw-3fgw
    PDB 3fh4-3g3r
    PDB 3g3s-3gxw
    PDB 3gyz-3hwt
    PDB 3hww-3ijp
    PDB 3imm-3k0g
    PDB 3k13-3l7x
    PDB 3l88-3max
    PDB 3mbb-3mr1
    PDB 3mty-3nu3
    PDB 3nu4-3ot1
    PDB 3ow2-3qwc
    PDB 3qx5-3tfr
    PDB 3tfs-3v6o
    PDB 3v72-4ag2
    PDB 4aga-4eae
    PDB 4ecn-4g8t
    PDB 4gdt-8icw
    PDB 8icx-9icy

Sodium borates






The anhydrous metaborate, NaBO2, is formed by fusing borax with sodium carbonate, being obtained in hexagonal prisms, m.p. 966° C., density 0.2571 between 17° and 97° C. When the syrup-like solution obtained by concentrating equivalent proportions of sodium hydroxide and boric acid or borax is allowed to crystallize over concentrated sulphuric acid, the tetrahydrate separates in triclinic crystals. The dihydrate and other hydrates have also been described. The aqueous solution of the metaborate has an alkaline reaction, due to hydrolytic dissociation. The orthoborate is formed by fusing boric anhydride with sodium peroxide.

The most important borate of sodium is disodium tetraborate or borax, Na2B4O7,10H2O, found in Thibet as the mineral tincal, and also in California. The native variety is purified by crystallization, but most of the borax of commerce is obtained by fusing native boric acid with sodium carbonate.

The anhydrous salt is obtained by heating the decahydrate, and is a white substance of density 2.367. Its melting-point is given as 561° C., 730° C., 741° C., and 878° C., the fused substance solidifying to a colourless, transparent, vitreous mass known as the " borax bead." In the melted state it dissolves metallic oxides, producing characteristic colorations, and finds application in analysis. It is also employed in soldering metals to remove the superficial layer of oxide, and to prevent oxidation during the process by excluding the air. Its specific heat is 0.229 between 17° and 47° C. (Kopp), and 0.2382 between 16° and 98° C. (Regnault). Its heat of formation is 748.1 Cal.

The decahydrate or ordinary borax forms monoelinic crystals of density 1.723 (Hassenfratz); or 1.694 at 17° C., and 1.728 at the temperature of liquid air (Dewar). Its specific heat is 0.385 between 19° and 50° C. A pentahydrate belonging to the rhombohedral division of the hexagonal system crystallizes above 60° C. Its density is 1.815. The pentahydrate is stable from 60° C., the transition-point from the decahydrate, to 125° C. At 130° C. the stable form is the trihydrate at 150° C. it is the dihydrate; and at 180° C. it is the monohydrate. The last molecule of water is retained up to 318° C.

By fusing borax with boron trioxide, two definite acid borates are produced. One of them has the formula Na2O,3B2O3, and melts at 694° C.; the other melts at 783° C., and has the formula Na2O,4B2O3. The crystallization of solutions with the composition ratio

Na2O:B2O3=1:5

yields a disodium pentaborate, Na2O,5B2O3,10H2O.

Sodium perborate, NaBO3,4H2O. - A perborate of the formula indicated is formed by the action of excess of hydrogen peroxide on a solution of borax and sodium hydroxide, and the action of a mineral acid or hydrogen peroxide on a mixture of sodium peroxide and boric acid:

2B(OH)3 + 2Na2O2+H2SO4+4H2O = 2(NaBO3,4H2O)+Na2SO4;
2B(OH)3+Na2O2+H2O2 + 4H2O=2(NaBO3,4H2O).

It is also produced in the electrolysis of an aqueous solution of sodium metaborate, or of sodium carbonate and borax. Alsgaard recommends electrolyzing a solution containing borax, sodium carbonate, sodium hydrogen carbonate, potassium dichromate, and sodium silicate with a copper pipe as cathode and a platinum anode, the current being 6 amperes at 7 to 8 volts, and the temperature 10° C. Foerster considers the formula NaBO2,H2O2,3H2O to be more in accord with the properties of the compound than NaBO3,4H2O.

Sodium perborate tetrahydrate is stable in air, but in aqueous solution it loses oxygen. The solution is alkaline in reaction. The velocity of decomposition and catalysis of sodium perborate have been studied by Seorgi and Nocentini. Addition of alcohol precipitates a salt, probably NaBO4, readily decomposed with evolution of oxygen either in the dry state or on solution in water. The tetrahydrate loses its water of crystallization, forming a stable monohydrate. At 15° C. the solubility is 2.55 grams NaBO3 in 100 grams of water. The salt finds application as a therapeutic agent, and is employed in bleaching. Its behaviour in solution is similar to that of hydrogen peroxide.

From a solution in water of sodium peroxide and boric acid another perborate, or " perborax," Na2B4O8,10H2O, separates. On solution in water it yields hydrogen peroxide. At 22° C. its solubility is 71 grams of Na2B4O8 in 100 grams of water, the solution being strongly alkaline.


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