Inorganic Chemicals

Formula: CH3COONH4; MW 77.08

Uses

Ammonium acetate is used for preserving meats; as a mordant in the dyeing of wool; in analytical chemistry for standardization of electrodes, and in titrations; also as a therapeutic diuretic and diaphoretic.

Physical Properties

White crystalline solid; deliquescent; melts at 114°C; decomposes at elevated temperatures; density 1.17 g/cm3 at 20°C, density of a 10% solution 1.022 g/mL, and a 50% solution 1.092 g/mL; very soluble in cold water (1,480 g/L at 4°C); also soluble in cold alcohol and acetone (78.9 g/L in methanol at 15°C); solution loses ammonia on standing and becomes acidic.

Preparation

Ammonium acetate is made by exact neutralization of acetic acid with ammonia to neutral pH (pH 7):

CH3COOH + NH3 →CH3COONH4

Instead of aqueous solutions, hot glacial acetic acid and anhydrous ammonia may be used. Ammonium acetate also is prepared by reaction of acetic acid with ammonium carbonate:

CH3COOH + (NH4)2CO3 → 2CH3COONH4 + CO2 + H2O

Reactions

Ammonium acetate forms an acid salt, ammonium acetate double salt, with hot acetic acid:

CH3COONH4 + CH3COOH → CH3COONH4 •CH3COOH

The acid salt readily dissolves in water and melts at 66°C. Water-insoluble lead iodide dissolves in  amonium acetate solution, lead acetate and ammonium iodide are formed:

PbI2 + 2CH3COONH4 → (CH3COO)2Pb + 2NH4I

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 : (NH4)2Cr2O7; MW 252.10

Synonym : ammonium bichromate

Uses

Ammonium dichromate is used in pyrotechnics; in photoengraving and lithography; as a source of pure nitrogen in the laboratory; and as a catalyst.

Physical Properties

Bright orange-red monoclinic crystals; odorless; hygroscopic; decomposes at 180°C; density 2.115 g/cm³ at 25°C; readily dissolves in water (26.67 g/100 g at 20°C).

Preparation

(NH4)2Cr2O7 may be prepared by the reaction of ammonia gas with chromic acid:

2NH3 + 2CrO3 + H2O → (NH4)2Cr2O7

or ammonium sulfate with sodium dichromate:

(NH4)2SO4 + Na2Cr2O7 → (NH4)2Cr2O7 + Na2SO4

Reactions

(NH4)2Cr2O7 decomposes at 180°C. On further heating to 225° C it begins to swell and dissociates exothermically, liberating nitrogen and water vapor, leaving behind a residue of chromium(III) oxide:

(NH4)2Cr2O7→N2+Cr2O3+4H2O

As an acid salt, its solution is acidic (pH 3.45 and 3.95 for a 10% and 1% solution, respectively). It undergoes acid reactions. Also, it undergoes double decomposition reactions, forming metal dichromates:

(NH4)2Cr2O7 + Pb(NO3)2 → PbCr2O7 + 2NH4NO3

As an oxidizing agent, it undergoes oxidation-reduction reactions with reducing agents at ambient and elevated temperatures.

Hazard

Ammonium dichromate is an irritant to skin. Inhalation of dusts can cause pulmonary irritation, perforation of the nasal septum and “chrome sores.” Ingestion can cause ulceration. It is also a flammable salt.