Inorganic Chemicals

Formula: NH4HCO3; MW 79.06

Synonyms: ammonium hydrogen carbonate; ammonium acid carbonate

Uses

Ammonium bicarbonate is used in preparing baking dough; in the production of ammonium salts; in heat-exchanger tubes as a scale-removing compound; in fire-extinguishing compositions; in cooling baths; in the manufacture of porous plastics and ceramics; and as a “smelling salt,” mixed with oil of lavender.

Physical Properties

White crystalline solid; prismatic crystal; faint odor of ammonia; stable at ambient temperature but decomposes on heating at 60°C; melts at 107.5°C on very rapid heating; density 1.586 g/cm3; vapor pressure 435 torr at 25°C; readily dissolves in water (21.6g/100g at 20°C, and 36.6g/100g at 40°C).
Manufacture Ammonium bicarbonate is made by passing carbon dioxide through an aqueous solution of ammonia in an absorption column or a packed tower:

NH3 + H2O + CO2 → NH4HCO3

In this process, ammonia solution flows countercurrent to the ascending stream of CO2. Crystals of ammonium bicarbonate precipitate out when the solution becomes sufficiently saturated. The crystals are filtered or centrifuged out of the mother liquor, washed, and air-dried. Pure product may be obtained by using high purity CO2. Alternatively, high purity ammonium bicarbonate may be obtained by subliming the product formed at relatively low temperatures.

Reactions

Ammonium bicarbonate decomposes to CO2, ammonia, and water vapor on heating; it liberates CO2 when treated with dilute mineral acids:

NH4HCO3 + HCl → NH4Cl + CO2 + H2O

It reacts with sulfates of alkaline-earth metals precipitating out their carbonates:

CaSO4 + 2NH4HCO3 → CaCO3 + (NH4)2SO4 + CO2 + H2O

The above reaction is applied in descaling calcium sulfate scale in heatexchanger tubes. Ammonium bicarbonate forms double salts with many other salts.

Formula: NH4HF2; MW 57.04

Synonym: ammonium hydrogen fluoride

Uses

NH4HF2 is used to solubilize silica and silicates in siliceous rocks of oil wells, thus to regenerate oil flow; as a neutralizer for alkalies in textile plants and commercial laundries; for removing stains from fabrics; for treating, polishing and rapid frosting of glass plates, window panes, picture frames, ampoules and optical lenses; to produce pure salts of metal fluorides; in treatment processes to prevent corrosion on magnesium and its alloys; in the preservation of wood; and in aluminum anodizing formulations.

Physical Properties

Orthorhombic or tetragonal crystals; etches glass; deliquescent; density 1.50 g/cm3; refractive index 1.390; melts at 125.6°C; very soluble in water; slightly soluble in alcohol.

Preparation

Commercial grade salt containing 1% NH4F is made by gas-phase reaction of one mole of anhydrous ammonia with two moles of hydrogen fluoride:

NH3 + 2 HF → NH4HF2

It may also be prepared in the anhydrous form by dehydration of ammonium fluoride solution, followed by thermal decomposition of dry crystals.

Reactions

Thermal dissociation produces ammonium fluoride and ammonia; at elevated temperatures products contain ammonia and hydrogen fluoride. It forms a colorless double salt, ammonium iron fluoride 3NH4F•FeF3, with iron, a reaction of commercial application for removing stains from fabric. It reacts with many metal oxides at elevated temperatures forming double fluorides:

2NH4HF2BeO→(NH4)2BeF4+H2O

6NH4HF2+Al2O3→2(NH4)2AlF6+3H2O

On further heating, the double fluorides decompose to metal fluorides, liberating ammonia and hydrogen fluoride:

(NH4)2BeF4→BeF2+2NH3+2HF

(NH4)3A1F6→A1F3+3NH3+3HF

The above reactions are employed commercially for obtaining metal fluorides in high purity. Similar reactions occur with many metal carbonates at elevated temperatures, producing double fluorides. The latter decompose to metal fluorides on further heating:

2NH4HF2+MgCO2→(NH4)2MgF4+CO2

(NH4)2MgF4→MgF2+2NH3+2HF

Analysis

Elemental composition: F 66.61%; H 8.83%; N 24.55% A measured amount of salt is thermally decomposed to ammonia and hydrogen fluoride. These gases liberated in stoichiometric amounts are

(NH4)2BeF4→BeF2+2NH3+2HF

(NH4)3A1F6→A1F3+3NH3+3HF

absorbed in excess standard sulfuric acid solution. Ammonia is measured by back titration of excess acid against a standard solution of caustic soda, using methyl orange indicator. Fluoride ion is measured with an ion-specific electrode. Ammonia may be collected and measured by alternative techniques (see Ammonia).

Formula: NH4Br; MW 97.94; ionic salt, cubic crystal

Uses

Ammonium bromide is used for photography in films, plates, and papers; in fireproofing of wood; in lithography and process engraving; in corrosion inhibitors; and in pharmaceutical preparations.

Physical Properties

White crystal or granule; strong saline taste; no odor; slightly hygroscopic; density 2.429 g/cm3 at 25°C; refractive index 1.712; sublimes at elevated temperatures: vapor pressure 54.75 torr at 300°C and 758.2 torr at 395°C; highly soluble in water: 60.6 g and 75.5 g/100 mL at 0° and 20°C, respectively - solubility increasing approximately 16 to 18 g/100 mL for every 20°C increase in temperature.

Thermochemical Properties

ΔHƒ°(s) –64.73 kcal/mol
ΔGƒ°(s) –41.9 kcal/mol
S° 27 cal/degree mol
Cρ 23 cal/degree mol

Preparation

Ammonium bromide is prepared by treating excess ammonia with bromine:

8NH3 + 3Br2 → 6NH4Br + N2

It may be also prepared by the reaction of ammonia and hydrobromic acid:

NH3 + HBr → NH4Br

NH4Br is also made by the reaction of ammonia with ferrous and ferric bromide, which may be obtained by passing aqueous bromine solution over iron filings.

2NH3 + FeBr2 + H2O → 2NH4Br + FeO
6NH3 + 2FeBr3 + 3H2O → 6NH4Br + Fe2O3

Reactions

Ammonium bromide exhibits acid reaction in aqueous solution; acts as an excellent acid in liquid NH3, undergoing neutralization reactions:

NH Br + NaNH3→NaBr + 2NH3

Contact with metal surfaces produces bromides of the metals; similarly reactions with metal hydroxide bases yield corresponding bromides:

2NH4Br + Ca(OH)2 →CaBr2 + 2NH3 + 2H2O

Ammonium bromide decomposes to ammonia and hydrogen bromide when heated at elevated temperatures:

NH4Br→ NH3+HBr

Chemical Analysis

Elemental composition: Br 81.58%, H 4.12%, N 14.30% Mixed with NaOH solution and distilled; distillate analyzed for ammonia by titration, colorimetry, or electrode method (see Ammonia and Ammonium chloride). Bromide portion of NH4Br in aqueous solution may be analyzed by ion chromatography, or by the colorimetry method in which red to violet color is produced upon treatment with chloramine–T, and phenol red at pH 4.5. The colorimetry test for bromide is subject to interference from oxidizing and reducing agents, chloride, and bicarbonate. NH4Br may then be determined stoichiometrically.

Formula: NH2COONH4; MW 78.07;

Synonyms: ammonium aminoformate; ammonium carbonate anhydride

Uses

Ammonium carbamate is used as an ammoniating agent. It occurs as a mixed salt with ammonium bicarbonate and carbonate.

Physical Properties

Colorless rhombic crystal; odor of ammonia; sublimes at 60°C; very soluble in cold water; decomposes in hot water; slightly soluble in alcohol; insoluble in acetone.

Preparation

Ammonium carbamate is prepared from dry ice and liquid ammonia:

CO2 + 2NH3 → NH2COONH4

Reactions

Decomposes on heating to ammonia and carbon dioxide; in contact with air at ambient temperatures, it loses ammonia, forming ammonium carbonate. In solution, it is partly hydrolyzed to carbonate.

NH2COONH4 + H2O → (NH4)2CO3

The carbamate is decomposed by acids and their salts.

Formula: (NH4)2CO3•H2O; MW 114.10; not available in pure form; crystalline products consist of double salts of ammonium carbonate, ammonium bicarbonate, and ammonium carbamate.

Synonyms: salt of hartshorn; sal volatile

Uses

Applications of ammonium carbonate are similar to those of ammonium bicarbonate. It is used in baking powder; in fire extinguishers; as mordant in dyeing; for washing and defatting wools; in tanning; in manufacture of rubber products; as a “smelling salt”; as a source of ammonia, and as an expectorant.

Physical Properties

Colorless or translucent hard crystalline mass or white cubic crystals or powder; sharp taste; odor of ammonia; decomposes at 58°C; slow decomposition at ambient temperatures; readily dissolves in cold water; decomposes in hot water; insoluble in liquid ammonia, alcohol and carbon disulfide.

Preparation

Ammonium carbonate is obtained by passing carbon dioxide into aqueous ammonia solution in a column or tower. Ammonia, carbon dioxide and water vapor are distilled and the vapors condensed into a solid crystalline mass. It also may be prepared by subliming a mixture of ammonium sulfate and calcium
carbonate.

Reactions

Ammonium carbonate slowly decomposes on exposure to air, or rapidly breaks down on heating to ammonia, CO2, and water; liberates CO2 on treatment with dilute mineral acids. It reacts with metals forming their carbonates. Reaction with hydriodic acid produces ammonium iodide; and forms ammonium oxalate with oxalic acid.