Inorganic Chemicals

Formula: Al(NO3)3; MW 213.00; the anhydrous salt is covalent; also occurs as hydrated salts, Al(OH)(NO3)2, Al(OH)2NO3, and the more stable nonahydrate, Al(NO3)3 •9H2O [7784-27-2]

Uses
The nonahydrate and other hydrated aluminum nitrates have many applications. These salts are used to produce alumina for preparation of insulating papers, in cathode tube heating elements, and on transformer core laminates. The hydrated salts are also used for extraction of actinide elements.

Physical Properties
White or colorless crystalline solid (nonahydrate – rhombic crystal); deliquescent; refractive index 1.54; melts at 73.5°C; decomposes at 150°C; highly soluble in cold water (63.7% at 25°C), decomposes in hot water, soluble in polar organic solvents.

Preparation
The nonahydrate is prepared by treating aluminum, aluminum hydroxide, aluminum oxide, or aluminous mineral with nitric acid. The nitrate is crystallized from the solution.

Reactions
Since Al(NO3)3 or its salt hydrates dissociates to Al3+ and NO3– ions in the aqueous solution, its reactions in solutions are those of Al3+ . It is partially hydrolyzed, producing H3O+ and thus accounting for the acidity of its solution in water. The products constitute a complex mixture of mono- and polynuclear hydroxo species.
Aluminum nitrate is soluble in bases, forming aluminates, [Al(OH)4(H2O)2]–. It decomposes to Al2O3 when heated at elevated temperatures.

Chemical Analysis
Elemental composition: Al 12.67%, N 19.73%, O 67.60%. Al may be analyzed by various instrumental techniques, including atomic absorption or emission spectroscopy, or colorimetry (see under Aluminum). The nitrate anion in aqueous phase may be measured by the NO3– ion selective electrode, ion chromatography, or reduction with cadmium or hydrazine, followed by colorimetric tests.

Formula: AlN; MW 40.99

Uses
Aluminum nitride is used in manufacturing of steel and in semiconductors.

Physical Properties
White crystalline solid, hexagonal; odor of ammonia in moist air; sublimes at 2000°C; melts in N2 atmosphere over 2200°C; density 3.26 g/cm3 ; decomposes in water, alkalies and acids

Thermochemical Properties

ΔH°ƒ(s)          –76.0 kcal/mol
ΔG°ƒ(s)          –68.6 kcal/mol
S°                  4.82 cal/degree mol
Cρ                 7.20 cal/degree mol

Preparation
Aluminum nitride may be prepared in the laboratory by heating powdered aluminum metal with nitrogen.

Commercially, it is made by heating an aluminous mineral, such as, bauxite with coal in a stream of nitrogen.

Chemical Reactions
The nitride reacts with water forming aluminum hydroxide and ammonia.

AlN + 3H2O ——›Al(OH)3 + NH3

The compound decomposes in alkalies and acids forming products of complex stoichiometry.

Analysis
Elemental composition: Al 65.82%, N 34.18%, the metal is determined by wet analysis or AA spectroscopy. NH3 liberated on hydrolysis may be determined by titration or colorimetry (see under Ammonia).

Formula: AlPO4; MW 121.95

Synonym: Aluminum orthophosphate

Occurrence and Uses
The compound occurs in nature as the mineral, berlinite. Also, it occurs in nature in minerals, amblygonite, [NaAl(PO4)(OH)]; augelite, [Al2(PO4)(OH)3]; lazulite, [(Mg,Fe)Al2(PO4)2(OH)2]; variscite [(Al,Fe3+)(PO4)•2H2O]; and wavellite, [Al3(OH)3•(PO4)2•5H2O]. It is used as flux for ceramics; as cement in combination with calcium sulfate and sodium silicate; and in the manufacture of special glasses. It is also used in dried gel and therapeutically as an antacid.

Physical Properties
White powdery solid (rhombic plate); the mineral berlinite (AlPO4) has hexagonal quartz-like structure; refractive index 1.546; mp > 1,500°C; density 2.566 g/cu3; insoluble in water and alcohol; Ksp 9.83×10–10 very slightly soluble in HCl or HNO3.

Thermochemical Properties

ΔH°ƒ(s)      –414.4 kcal/mol
ΔG°ƒ(s)      –368.7 kcal/mol
S°             166.6 cal/degree mol
Cρ            22.27 cal/degree mol

Preparation
It is prepared by treating sodium aluminate with phosphoric acid.

NaAlO2 + H3PO4 ——›AlPO4 + NaOH + H2O

 It may be prepared by slowly adding (with stirring) ammonium phosphate (0.2M) to a solution of aluminum sulfate (0.1M).

Al2(SO4)3 + 2(NH4)3PO4 ——› 2AlPO4 +3(NH4)2SO4

The compound may, alternatively, be prepared by the reaction of aluminum sulfate with sodium phosphate.

Al2(SO4)3 + 2Na3PO4 ——› 2AlPO4 +3Na2SO4

Formula: Al2(SO4)3; MW 342.14

Occurrence and Uses
It occurs in nature in minerals; alunite, KAl3(SO4)2(OH)6 and natroalunite, NaAl3(SO4)2(OH)6. The anhydrous salt is used in food applications.

Physical Properties
White powder; refractive index 1.47; density 2.71 g/cm3; mp 770°C (decomposes); hygroscopic; readily soluble in water (31% at 0°C; solubility increases with temperature 98% in boiling water); soluble in dilute mineral acids; slightly soluble in alcohol.

Preparation
The anhydrous salt may be obtained by slow and progressive heating of commercial hydrated salt, Al2(SO4)3 •18H2O. Most water molecules are lost at heating between 250 to 420°C. The last three water molecules are lost between 250 to 420°C at a heating rate of 10°C/min.

Chemical Reactions
The compound decomposes to γ−alumina and SO3 when heated between 580 and 900°C. It combines with water forming hydrated salts of various compositions. Produces calcium aluminate with evolution of SO3 when calcined with CaCO4, (Bayliss, N. S. 1945. J and Proc. Austral. Chem. Inst., 12, 127)

Al2(SO4)3 + CaSO4 ——› Ca(AlO2)2 + 4SO3

Reacts with NaHCO3 in aqueous solution, forming fire-extinguishing foams, producing CO2, (Albert K. 1937. French Pat. 820,492, November 12, 1937)

Al2(SO4)3 + 6NaHCO3 ——› 2 Al(OH)3 + 3Na2 SO4 + 6CO2

Reaction with ammonium phosphate yields AlPO4 (see Aluminum phosphate, preparation)

Analysis
Elemental analysis: Al 15.77%; O 56.12%; S 28.11%. Al may be determined by colorimetric method or by atomic absorption or emission spectrophotometry; sulfate may be determined by BaCl2 precipitation method in the aqueous solution of the salt.

Formula: Al2(SO4)3 18H2O; MW 648.41

Synonyms: alum, cake alum (the term alum also refers to aqueous solutions of this substance, as well as other hydrate salts containing varying number of waters of crystallization; also the term alum applies to a whole class of sulfate double salts, such as potassium aluminum sulfate or ammonium aluminum sulfate.)

Uses
The compound is used heavily in the paper industry. In its acidic solution form, which contains a slight excess of H2SO4, it is used for pH control of pulp slurries, treatment of process waters, setting of dyes and also for precipitating dissolved resin for setting the size on the fibers. In slight basic form (containing a slight excess of Al2O3), it is used for treatment of drinking and waste waters (e.g., for reducing phosphorus content). Other major applications include dyeing, tanning, catalysts, modification of concrete, and in the manufacture of various chemicals and pharmaceutical products.

Physical Properties
White crystal; sweet taste; density 1.62 g/cm3: decomposes at 86.5°C; soluble in water.

Preparation
Prepared from bauxite, kaolin or aluminum compounds on reaction with H2SO4. The insoluble silicic acid is filtered out; the hydrate salt forms on crystallization.