SODIUM CARBONATE CAS N°: 497-19-8 - UNEP Chemicals

OECD SIDS SODIUM CARBONATE
1. IDENTITY
Name: Sodium carbonate
CAS number: 497-19-8
EINECS number: 207-838-8
Molecular formula: Na2CO3
Molecular weight: 106
Synonyms:
SIDS Initial Assessment Report
A synonym, which is widely used, is soda ash. Other synonyms are
carbonic acid disodium salt, disodium carbonate, calcined soda
(Clayton and Clayton, 1993; The Merck Index, 1983; Johnson and
Swanson, 1987).
In addition to the anhydrous form, the monohydrate form (CAS nr. 5968-11-6) and the decahydrate
form (CAS nr. 6132-02-1) do exist and are placed on the market in very small quantities (compared
to the anhydrous form). Sodium carbonate decahydrate is known as sal soda or washing soda.
Although sodium carbonate monohydrate has a different CAS number than anhydrous sodium
carbonate, several studies on the sodium carbonate monohydrate have been included in this dossier
because the intrinsic properties are expected to be similar to the anhydrate.
1.1 Composition
Sodium carbonate is a white, crystalline and hygroscopic powder with a purity of > 98 %. There are
two forms of sodium carbonate available, light soda and dense soda. Impurities of sodium carbonate
may include water (< 1.5 %), sodium chloride (< 0.5 %), sulphate (< 0.1 %), calcium (< 0.1 %),
magnesium (< 0.1 %) and iron (< 0.004 %). The purity and the impurity profile depends on the
composition of the raw materials, the production process and the intended use of the product. For
example the purity of the pharmaceutical grade must be higher than 99.5 % in Europe
(Pharmacopée Européenne, 1996).
1.2 Physical chemical properties
Sodium carbonate has a melting point of 851°C (CRC Handbook, 1986; The Merck Index, 1983), it
decomposes when heated at > 400 °C and therefore a boiling point cannot be determined. Sodium
carbonate is an inorganic salt and therefore the vapour pressure can be considered negligible. Its
density is 2.532 (20°C) and its water solubility is 71 g/l water at 0°C, 215 g/l water at 20°C and 455
g/l water at 100°C (CRC Handbook, 1986). The octanol water partition coefficient (log Pow) is not
relevant for an inorganic substance which dissociates. The average particle size diameter (d50) of
light sodium carbonate is in the range of 90 to 150 µm and of dense sodium carbonate is in the
range of 250 to 500 µm.
Sodium carbonate is a strong alkaline compound with a pH of 11.6 for a 0.1M aqueous solution
(The Merck Index, 1983; Johnson and Swanson, 1987). The pKa of CO3 2- is 10.33, which means
that at a pH of 10.33 both carbonate and bicarbonate are present in equal amounts.
UNEP PUBLICATIONS 7