Inorganic Chemicals

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 : (NH4)2HPO4; MW 132.07;

Synonyms: diammonium hydrogen phosphate; secondary ammonium phosphate

Uses
Dibasic ammonium phosphate is used as a fertilizer; as a fire extinguisher; a flame retardant for plywood, papers, and fabrics; to prevent afterglow in matches; in purifying sugar; as a flux for soldering tin, copper, zinc and brass; and to control precipitation of alkali-soluble or acid-insoluble colloidal dyes on wool.

Physical Properties
Colorless monoclinic crystal; saline taste; refractive index 1.52; density 1.619 g/cm³; melts at 155°C (decomposes); very soluble in water (57 g/100 g at 10°C and 106.7g/100g at 70°C, respectively); insoluble in alcohol, acetone, and liquid ammonia.

Preparation
is made by reacting ammonia with phosphoric acid:

Reactions
Heating at 70°C results in decomposition to monoammonium phosphate and ammonia:

A boiling, dilute solution of diammonium phosphate evolves ammonia (the pH of the solution decreases), which also occurs slowly at ambient temperatures. The solid and its solution create an ammonia vapor pressure. Reactions with mineral acids produce the corresponding ammonium salts.