Aluminum salts final content: chapter 2.1

2. Summary of information critical to assessment of toxic under CEPA 1999

2.1 Identity and physical/chemical properties

Aluminum chloride is also known as aluminum trichloride, aluminum chloride (1:3) and trichloroaluminum (Agency for Toxic Substances and Disease Registry (ATSDR) 2006). It has the Chemical Abstracts Service (CAS) registry number 7446-70-0 and a chemical formula of AlCl3. In its hydrated form, AlCl3·6H2O, it is called hexahydrated aluminum chloride (CAS No. 7784-13-6). Trade names include Aluwets, Anhydrol and Drichlor.

Synonyms for aluminum nitrate include aluminum trinitrate and aluminum (III) nitrate (1:3). The CAS registry number is 13473-90-0 and the chemical formula is Al(NO3)3. The nonahydrate aluminum nitrate, Al(NO3)3·9H2O (CAS No. 7784-27-2), is the stable form of this compound.

Aluminum sulphate can also be identified as alum, alumsulphate (2:3), aluminum trisulphate, dialuminum sulphate and dialuminum trisulphate. The CAS registry number for aluminum sulphate is 10043-01-3 and the chemical formula is Al2(SO4)3. Alum is often represented as Al2(SO4)3·14H2O. It may be found in different hydrated forms. The commercial product, called cake alum or patent alum, is an octadecahydrate aluminum sulphate, Al2(SO4)3·18H2O.

In addition to these three compounds, aluminum polymers such as polyaluminum sulphate (PAS) and polyaluminum chloride (PAC) are used in water treatment. The general formula for PAS is Ala(OH)b(SO4)c, where b + 2c = 3a; for PAC, the general formula is Ala(OH)bClc, where b/a is usually about 2.5 (e.g., Al2(OH)5Cl). Mixed aluminum polymers may also be used; their general formula is Ala(OH)bClc(SO4)d, and b/a varies between 0.4 and 0.6.

Physicochemical properties of the three aluminum salts are presented in Table 2.1.

Table 2.1: Physicochemical Properties of Aluminum Chloride, Aluminum Nitrate and Aluminum SulphateFootnote a
Property Aluminum chloride Aluminum nitrate Aluminum sulphate
CAS No. 7446-70-0 13473-90-0 10043-01-3
Molecular formula AlCl3 Al(NO3)3 Al2(SO4)3
Molecular weight 133.34 213.00 342.14
Colour White when pure, ordinarily gray or yellow to greenish ColourlessFootnote b White, lustrous
Physical state White hexagonal deliquescent or moisture sensitive plates Rhombic crystalsFootnote b Crystals, pieces, granules or powder
Density (g/mL) 2.48 No data 1.61
Melting point (°C) 194 at 527 kPa 73Footnote b Decomposes at 770
Boiling point (°C) 182.7
(1.00×105 Pa or 752 mm Hg; sublimation temperature)
Decomposes at 135 °CFootnote b No data, substance has no boiling point
Solubility in water
(g/100 mL)
69.86 (15°C)
(Reacts violently with water)
63.7 (25°C) 36.4 (20°C)
Solubility in other solvents Soluble in benzene, carbon tetrachloride, chloroform Very soluble in alcohol; slightly soluble in acetone
almost insoluble in ethyl acetate, pyridineFootnote b
Insoluble in ethanol
pH No data Aqueous solution is acidic No data
Vapour pressure (Pa) 100
No data 0 (20°C)
substance has no vapour pressure
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