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 carbonate, Na2CO3






The carbonate is present in the ashes of sea-plants, its principal source prior to the French Revolution, when Le Blanc devised a method for its production. It is also found in the form of solid deposits, and in solution in many natural waters. Pozzi-Escot believes the Peru deposits to have originated in the reduction to sodium sulphide, by means of plants and algae, of sodium sulphate dissolved from the soil, the sulphide formed being converted into sodium carbonate or sodium hydrogen carbonate by the action of carbon dioxide from the air, or from the decomposition of vegetable matter.

Sodium carbonate is manufactured from sodium chloride by three processes: Le Blanc's process, Solvay's ammonia-soda process, and the electrolytic process.

Le Blanc's Process

This process involves three stages: the conversion of sodium chloride into sodium sulphate, or " salt-cake process "; the reduction of the sulphate to sulphide by means of carbon, and the conversion of the sulphide into sodium carbonate by the action of calcium carbonate, or " black-ash process "; and the extraction of the sodium carbonate with water, or " lixiviation process ":

NaCl+H2SO4=NaHSO4+HCl;

NaCl+NaHSO4 =Na2SO4+HCl;

Na2SO4+2C=Na2S+2CO2;

Na2S+CaCO3 = Na2CO3+CaS.

The salt-cake process takes place in two stages, the reaction represented by the second equation being carried on at a higher temperature in a reverberatory furnace. The hydrochloric acid constitutes a valuable by-product.

The sulphate prepared by the salt-cake process is pulverized, and mixed with an equal weight of chalk and half its weight of coal or coke. The mixture is then fused in a rotatory furnace. At first only carbon dioxide is evolved, but at the end of the operation carbon monoxide is generated, and burns as it escapes into the atmosphere:

2CaCO3+2C =2CaO+4CO.

The sodium carbonate is lixiviated with water to separate it from the calcium sulphide or " alkali-waste," and from other impurities such as sodium chloride, sulphate, silicate, and aluminate; calcium oxide, sulphite, and thiosulphate; iron oxide; and alumina.

Ammonia-soda Process

This process is said to have been devised by the apothecary Gerolamo Forni in 1836. It was perfected by Solvay, and on the continent of Europe it has largely displaced the older Le Blanc process. A solution of sodium chloride is treated alternately with ammonia and carbon dioxide under pressure, sodium hydrogen carbonate separating out from the concentrated solution of ammonium chloride. On heating, the sodium hydrogen carbonate is converted into sodium carbonate, the evolved carbon dioxide being utilized again in the formation of sodium hydrogen carbonate. The ammonia is recovered from the ammonium-chloride solution by distilling it with lime obtained as a by-product in the generation of the carbon dioxide from limestone. The reactions 1 involved are represented by the equations

2NaCl + 2NH3+2CO2+2H2O = 2NH4Cl+2NaHCO3;

2NaHCO3=Na2CO3+CO2+H2O;

CaCO3=CaO + CO2;

2NH4Cl + CaO = 2NH3 + CaCl2+H2O.

The process yields a purer initial product than the Le Blanc method, but has the disadvantage of leaving the chlorine of the sodium chloride in the form of calcium chloride, for which the demand is limited.

The equilibrium of the four salts sodium chloride, sodium hydrogen carbonate, ammonium chloride, and ammonium hydrogen carbonate has been studied by Toporescu, and he has constructed a diagram to facilitate calculation of the proportion of each salt which will crystallize on progressive evaporation of a solution of known initial composition. His diagrammatic method has been applied by Le Chatelier to ascertaining the proportion of water or salt which must be added to get the maximum yield of pure sodium hydrogen carbonate under manufacturing conditions.

The use of sodium nitrate as a substitute for sodium chloride in the ammonia-soda process has been studied by Fedotiew and Koltunow.

Electrolytic Process

The production of sodium carbonate by the electrolysis of sodium-chloride solution is gradually supplanting the older methods. The solution of sodium hydroxide formed is converted into carbonate by the action of carbon dioxide, the sodium hydrogen carbonate formed being decomposed by heat.

Sodium carbonate is also manufactured to some extent from other materials, such as cryolite, a double fluoride of sodium and aluminium found in Greenland, and sodium nitrate.

Sodium carbonate Properties

Anhydrous sodium carbonate is a white solid, density 2.476, m.p. 851° to 853° C. Its specific heat is 0.246 between 18° and 48° C. (Kopp), and 0.2728 between 16° and 98° C. (Regnault). Its heat of formation from the elements is given as 272.64, 270.8, or 271.97 Cal.

Solubility Na2CO3
Solubility-curve of sodium carbonate
Sodium carbonate forms three hydrates. The decahydrate is monoclinic, and has the density 1.455, other values being 1.446 at 17° C. and 1.493 at the temperature of liquid air. At 20° C. 100 grams of water dissolve 21.4 grams, reckoned as Na2CO3. The heptahydrate appears to exist in both a rhombic and a metastable rhombohedral form, but only between narrow limits of temperature. Its solubility diminishes with rise of temperature. The solubility of the monohydrate at 50° C. is 47.5 grams Na2CO3 in 100 grams of water. The transition-points of the hydrates are given by Wells and McAdam: 10 to 7 (D), 32.0° C.; 7 to 1 (F), 35.37° C.; 10 to 1 (intersection CD and GF), 32.96° C. Some of their solubility-data are given in the table, and the solubility-curve in Fig.

The transition-temperature of the decahydrate to the heptahydrate is given by Richards and Fiske as 32.017° C.

According to Berzelius, and also Schindler, the decahydrate in air at 12.5° C. becomes transformed into a pentahydrate. The existence of other hydrates described is even more doubtful. The boiling solution of sodium carbonate absorbs carbon dioxide from the atmosphere. Dubovitz Jpund that exposure of the solid carbonate to atmospheric carbon dioxide and moisture for thirteen days produced between 15 and 20 per cent, of the primary salt, NaHCO3, and that with a large excess of carbon dioxide and moisture complete conversion could be attained.


© Copyright 2008-2012 by atomistry.com