Sodium carbonate
Sodium carbonate (also known as washing soda, soda ash and soda crystals).

Chemical formule : Na2CO3
(O = 45,29 %, Na = 43,38 %, C = 11,33 %)

Molar mass = 105,9884 ± 0,0017 g·mol-1

Hygroscopic white powder (anhydrous), it is the sodium salt of carbonic acid [CO3, H2O]; in everyday language, also known as washing soda, because of its sodium content and its usually crystalline form. However, this should not be confused with salt Caustic soda NaOH, or with sodium bicarbonate NaHCO3.

Sodium carbonate crystallizes from water to form three different hydrates:

  1. sodium carbonate decahydrate (natron)
  2. sodium carbonate heptahydrate (not known in mineral form)
  3. sodium carbonate monohydrate (thermonatrite)

Production (natural) :
Sodium carbonate is soluble in water, and can occur naturally in arid regions, especially in mineral deposits (evaporites) formed when seasonal lakes evaporate. Deposits of the mineral natron* have been mined from dry lake bottoms in Egypt since ancient times, when natron was used in the preparation of mummies and in the early manufacture of glass. The anhydrous mineral form of sodium carbonate is quite rare and called natrite.
*evaporite rock containing sodium carbonate decahydrate (Na2CO3·10H2O) and sodium bicarbonate (NaHCO3).

Formerly, it is also produced from the ashes of seaweed (kelp or seaweed in Brittany) or plants (Salicornia in the Mediterranean).

Synthetic product.
Solvay process (1870) which produces sodium carbonate from salt and chalk supplanted Leblanc process (developed in 1789) as cleaner and less expensive.

Main Features

Anhydrous product
Na2CO3 %
80 to 97
Volumetric mass density (20°C)  
2500 kg/m3
Melting point

Maximum solubility in water
(soft) as a function of the temperature (Na2CO3 % by weight ) :

Solutions at 50g/L :

A formulation for water treatment
Reaction mechanism of lime with aggressive CO2 (simplified equations):

Na2CO3 + CO2 + H2O >>> 2 NaHCO3
....106.........44 .....................2x84 or[100 mg/L as CaCO3 (10°F<TAC)]

Thus, to neutralize 1 mg of CO2, it is necessary to use (106/44)= 2.41 mg de Na2CO3, which form (168/44)=3.82 mg of sodium bicarbonate NaHCO3, and therefore also the neutralization of 1 mg /L to form CO2 (10/44) = 0.2273 °F/l as TAC (i.e.2.273 mg CaCO3/L of Alkalinity).

Note: if the calculated dose is a reagent for 100% purity, it is necessary to correct this dose to entering the purity of the commercial product.

Standard products used for the production of drinking water: French Official Bulletin - Sodium carbonate : NF EN 897.

Effects on the environment.

Sodium carbonate is not toxic to the environment. But it can be irritating to the skin and so it is best handled with gloves.


Sources : personal and Wikipedia, the free encyclopedia.

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