ALUMINUM PHOSPHATE
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
CÏ Â Â Â Â Â Â Â Â Â Â 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
Tags: AlPO4; MW 121.95, ALUMINUM, ALUMINUM PHOSPHATE, PHOSPHATE
