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 hydroxide, NaOH






The pure hydroxide can be prepared in the laboratory by dissolving sodium in water and evaporating the solution, or by the electrolysis of commercial sodium hydroxide in aqueous solution with a mercury cathode, the amalgam formed being decomposed by water. A solution free from carbonate can be obtained in the laboratory by suspending metallic sodium in a layer of ether floating on the surface of water. The metal dissolves slowly in the water present in the ether, and the sodium hydroxide passes into the bottom aqueous layer. The hydroxide is manufactured by the electrolysis of a solution of sodium chloride; and, according to van Laer, an economical yield can be obtained directly by the electrolysis with a suitable diaphragm of a solution of sodium carbonate containing nitrate or sulphate of sodium to hinder the formation of sodium hydrogen carbonate. Sodium hydroxide is also produced industrially by the much older method of decomposing sodium carbonate with slaked lime, a reversible reaction:

Na2CO3+Ca(OH)2 ⇔ 2NaOH+CaCO3.

The solution of sodium hydroxide is evaporated in iron vessels, the finished product being marketed in the form of sticks or powder, or in cylindrical blocks of about 6¾ cwt. enclosed in iron drums. Slaked lime also decomposes sodium sulphate with production of sodium hydroxide, and the effect on the yield of the temperature and the dilution of the solution has been studied by Neumann and Karwat.

Sodium hydroxide is a white substance of density 2.130. It dissolves readily in both water and alcohol. It is very stable, melting at 318.4° C. and at a higher temperature volatilizing without decomposition. Admixture with other substances lowers the melting-point. The mixture containing 58.4 per cent, of potassium hydroxide melts at 167° C., that with 20.7 per cent, of a mixture of 48.5 per cent, of sodium carbonate and 51.5 per cent, of potassium carbonate at 265° C., and that with 17 per cent, of sodium carbonate at 280° C. For the latent heat of fusion per mol., Hevesy gives 1.602 Cal. Its hygroscopic character causes it to liquefy on exposure to air, but it is converted into solid carbonate by the action of atmospheric carbon dioxide. The percentage of water in fused samples varies between 0.9 and 1.2, the average being 1.1.

Freezing-points of NaOH
Freezing-points of solutions of sodium hydroxide.
Some of Pickering's data for the solubility are plotted in figure.

The curve indicates the existence of several hydrates, including two tetrahydrates, a freezing at 7.57° C., and β freezing at -1.7° C. The monohydrate melts at 64.3° C. For its density Gerlaeh gives 1.829. At 12° C. it is transformed into the dihydrate, which at a concentration of 45.5 per cent, of sodium hydroxide is in equilibrium at 5° C. with a 3.5 hydrate, 2NaOH,7H2O, as is also the α-tetrahvdrate at the same temperature and a concentration of 32 per cent, of sodium hydroxide. At -17.7° C. the α-tetrahydrate changes to the pentahydrate, and this form at -24° C. to the heptahydrate. The saturated solution in contact with the solid boils at 314° C.

The specific heat of the anhydrous hydroxide is given by Blumcke as 0.78 between 0° and 98° C. The mean molecular refraction of the molten hydroxide between 320° and 440° C. is 5.37. The heat of formation from the elements is given by de Forcrand as 103.10 Cal., and that from the solid monoxide and liquid water as 36.50 Cal. For the former, Rengade gives 1019 Cal., and in solution 111.8 Cal.; for the heat of formation in dilute solution from sodium and water he gives 44.1 Cal. The heat of solution is given by Thomsen as 9.94 Cal., and by Berthelot as 9.8 Cal. The heat of dilution has also been studied by both these investigators. The heat of formation of the monohydrate is given by Berthelot as 3.25 Cal. The heat of neutralization of the hydroxide by mineral acids has been investigated by Richards and Rowe.

At ordinary temperatures an aqueous solution of sodium (or potassium) hydroxide dissolves sulphur, forming sulphide, polysulphides, thiosulphate, and sulphite. The reaction is very complex, but Calcagni thinks that the sulphide is probably formed first, thiosulphate next, and then polysulphides. Finally, sulphite is produced by decomposition of the thiosulphate. With concentrated solutions part of the sulphur probably dissolves without entering into combination. Ammonium hydroxide of density 0.888 behaves similarly.

When heated in copper vessels at temperatures between 350° and 600° C. in contact with air, sodium hydroxide has been observed to dissolve up to 0.73 per cent, of its weight of copper. The action on iron is less, and on nickel least of all.

Other properties of aqueous solutions have been studied, such as the density, vapour-pressure, boiling-point, molecular depression of the freezing-point, electric conductivity, electrolytic dissociation, refractivity, viscosity, diffusion, dissociation-pressure, and power of dissolving gases.


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