AMMONIUM PHOSPHATE, MONOBASIC / AMMONIUM SULFATE 43
AMMONIUM PHOSPHATE, MONOBASIC
[7722–76–1]
Formula: (NH4)H2PO4; MW 115.03;
Synonyms: ammonium dihydrogen phosphate; ammonium biphosphate; primary ammonium phosphate
Uses
Monobasic ammonium phosphate is used in fire extinguishers; as a flame retardant for papers, plywoods, and fabrics; in baking mixtures; and in fermentation process.
Physical Properties
White crystalline powder; odorless; density 1.80 g/cm3; readily dissolves in water (40 g/ 100 g); pH of 0.2 molar solution 4.2; slightly soluble in alcohol; insoluble in acetone.
Preparation
Preparative method similar to its dibasic salt; obtained by reaction of equimolar amounts of ammonia and phosphoric acid:
NH3 + H3PO4 → (NH4)H2PO4
Reactions
Thermal decomposition produces ammonia and phosphoric acid; reaction with sulfuric acid produces ammonium hydrogen sulfate:
(NH4)H2PO4 + H2SO4 → (NH4)HSO4 + H3PO4
(NH4)H2PO4 decomposes under strong oxidizing conditions producing nitrogen, water, and phosphorus pentaoxide.
AMMONIUM SULFATE
[7783–20–2]
Formula: (NH4)2SO4; MW 132.14;
Occurrence and Uses
Ammonium sulfate occurs in trace concentrations in the upper atmosphere. It is widely used as a fertilizer for rice and other crops. It is a source of sulfur for the soil. It is also used as an additive to supply nutrient nitrogen in fermentation processes (e.g., yeast production from molasses). It also is used for fireproofing timber and plastics, and in treatment of hides, and leather production.
44 AMMONIUM SULFATE
Physical Properties
White crystalline solid; orthorhombic crystal; density 1.769 g/cm3 at 20°C; melts between 511 to 515°C (in a closed system): however, in an open system, it melts with decomposition at 280°C; readily dissolves in water (solubility, 70.6 g and 104 g per 100 g water at 0°C and 100°C, respectively); insoluble in acetone, alcohol and ether.
Thermochemical Properties
∆Η°ƒ |
–282.5 kcal/mol |
∆G°ƒ |
–215.6 kcal/mol |
S° |
52.6 cal/degree mol |
Cρ |
44.8 cal/degree mol |
Manufacture
Ammonium sulfate is made by reacting synthetic ammonia (or by-product ammonia from coke-ovens) with sulfuric acid:
2NH3 + H2SO4 → (NH4)2SO4
A mixture of ammonia gas and water vapor is introduced into a reactor (“saturator”) that contains a saturated solution of ammonium sulfate and about 2 to 4% free sulfuric acid at 60°C. Concentrated sulfuric acid is added continuously to keep the solution acidic, and to retain its level at 2 to 4% free acid. The heat of reaction keeps reactor temperature at 60°C. Ammonium sulfate formed crystallizes out of its saturated solution in the reactor.
Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all water present in the system, forming a powdery salt.
Ammonium sulfate also is manufactured from gypsum salt, CaSO4·2H2O. Finely divided gypsum is added to ammonium carbonate solution. Calcium carbonate precipitates out, leaving ammonium sulfate in solution.
(NH4)2CO3 + CaSO4 → (NH4)2SO4 + CaCO3
Reactions
Ammonium sulfate decomposes upon heating at 100°C in an open system, forming ammonium bisulfate, NH4HSO4. As a salt of a strong acid and weak base, its solution is acidic; pH of 0.1M solution is 5.5.
In aqueous solution the reactions are those of NH4+ and SO24–ions. For example, addition of barium chloride, BaCl2 precipitates out barium sulfate, BaSO4. The filtrate on evaporation yields ammonium chloride, NH4Cl.
AMMONIUM SULFIDE 45
(NH4)2SO4 forms many double salts (ammonium metal sulfates) when its solution is mixed with equimolar solutions of metal sulfates and the solution is slowly evaporated. Such double metal sulfates include ammonium cobaltous sulfate, (NH4)2Co(SO4)2; ferric ammonium sulfate, (NH4)2Fe(SO4)2, ammonium nickel sulfate, (NH4)2Ni(SO4)2; and ammonium cerous sulfate, NH4CeSO4.
Chemical Analysis
Elemental composition: H 6.10%, N 21.20%, O 48.43%, S 24.27%.
A small amount of solid may be dissolved in water and ammonium ion determined by the ion-selective electrode method, or miscellaneous colorimetric or titrimetric procedures (see Ammonia). Sulfate ion may be determined by ion chromatography.
AMMONIUM SULFIDE
[12135–76–1]
Formula: (NH4)2S; MW 68.143 Synonym: ammonium monosulfide
Uses
Ammonium monosulfide is used in photographic developer; to apply patina to bronze; and in textile manufacture.
Physical Properties
Unstable, decomposes at ambient temperature; forms yellow crystals below –18°C; hygroscopic; soluble in water and alcohol, very soluble in liquid ammonia.
Thermochemical Properties
∆Η°ƒ (aq) |
–55.4 kcal/mol |
∆G°ƒ |
–17.4 kcal/mol |
S° |
50.7 cal/degree mol |
Preparation
(NH4)2S is obtained from reacting hydrogen sulfide with excess of ammonia:
H2S + 2NH3 → (NH4)2S
Reactions
Ammonium sulfide decomposes to ammonia and ammonium hydrosulfide:
46 AMMONIUM THIOCYANATE
(NH4)2S → NH3 + NH4HS
At elevated temperatures it forms polysulfides; also, it combines with sulfur, forming ammonium polysulfide:
(NH4)2S + 2S → (NH4)2S3
Ammonium sulfide forms ammonium chloride with HCl and ammonium nitrate with nitric acid, respectively.
Chemical Analysis
Elemental composition: H 11.83%, N 41.11%, S 47.05%. It may be analyzed by measuring its decomposition gaseous products, ammonia and hydrogen sulfide, either by gas chromatography using an FID or a TCD; or by selective ion electrode or colorimetric techniques.
AMMONIUM THIOCYANATE
[1762–95–4]
Formula: NH4SCN; MW 76.122
Uses
Ammonium thiocyanate is used in the manufacture of herbicides, thiourea, and transparent artificial resins; in matches; as a stabilizing agent in photography; in various rustproofing compositions; as an adjuvant in textile dyeing and printing; as a tracer in oil fields; in the separation of hafnium from zirconium, and in titrimetric analyses.
Physical Properties
Crystalline solid forming monoclinic crystal; hygroscopic; melts at 149.6°C; decomposes at 170°C; density 1.305 g/cm3; highly soluble in water (128 g/100 mL at 0°C); soluble in liquid ammonia, alcohol, and acetone.
Manufacture
Ammonium thiocyanate is made in the United States by the reaction of carbon disulfide with aqueous ammonia. Ammonium dithiocarbamate is formed as an intermediate in this reaction, which upon heating, decomposes to ammonium thiocyanate and hydrogen sulfide.
CS2 + 2NH3(aq) → NH2C(=S)SNH4 → NH4SCN + H2S
Ammonium cyanate also may be prepared by direct sulfurization of ammonium cyanide.
NH4CN + S heat→ NH4SCN
Chemical Reactions
Ammonium thiocyanate is stable in air; however, upon heating it isomerizes to thiourea: