Inorganic Chemicals

Formula: NH4Cl; MW 53.49

Synonym: Sal ammoniac

Occurrence and Uses

Ammonium chloride occurs in nature in crevices near volcanoes. Also, it is found in smoke when burning dry camel or donkey dung as fuel. Important applications of this compound include the manufacture of dry cells for batteries; as a metal cleaner in soldering; as a flux in tin coating and galvanizing; in fertilizers; in pharmaceutical applications as a diuretic, or diaphoretic expectorant; and as an analytical standard in ammonia analysis. Also, it is used in freezing mixtures; washing powders; lustering cotton; in safety explosives and in dyeing and tanning.

Physical Properties

Colorless cubic crystals or white granular powder; saline taste; odorless; hygroscopic; does not melt but sublimes on heating at 340°C; vapor pressure 48.75 torr at 250°C and 251.2 torr at 300°C; density 1.5274 g/cm3 at 25°C; refractive index 1.642; readily dissolves in water, solubility: 229 g and 271 g/L solution at O°C and 20°C, respectively; solubility lowered by alkali metal chlorides and HCl; dissolution lowers the temperature of the solution; sparingly soluble in alcohols (6 g/L at 19°C) and soluble in liquid NH3; insoluble in acetone and ether.

Thermochemical Properties

ΔΗ°ƒ(s) –75.15 kcal/mol
ΔΗ°ƒ(s) [NH3(g) + HCl(g)] –41.9 kcal/mol
ΔG°ƒ(s) –48.51 kcal/mol
S° 22.6 cal/degree mol
Cρ 20.1 cal/degree mol
ΔH°subl (1 atm) 39.6 kcal/mol

Manufacture

Ammonium chloride is produced as a by-product in the Solvay process for manufacture of sodium carbonate:

NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl

NaHCO3 precipitate is filtered out of solution while NH4Cl is obtained by crystallization followed by washing and drying. Ammonium chloride also is produced from spent calcium chloride liquor obtained in ammonia-soda process:

CaCl2 + 2NH3 + CO2 + H2O → Na2SO4 + 2 NH4Cl

It also is made by heating a mixture of slight excess of NaCl solution with ammonium sulfate. The filtrate containing NH4Cl is concentrated and cooled.

NH4Cl crystallizes:

(NH4)2SO4 + 2NaCl → Na2SO4 + 2 NH4Cl

It is produced by direct neutralization reaction of NH3 and HCl combined as gaseous mixtures.

NH3(g) + HCl(g) → NH4Cl(s)

Reactions

NH4Cl is acidic in aqueous solution: the pH of 1%, 3%, and 10% solution at 25°C are 5.5, 5.1 and 5.0, respectively. (Merck 1996. The Merck Index, 12th ed. Rahway, NJ: Merck & Co.) It loses ammonia and becomes more acidic on prolonged exposure or storage. It reacts with iron, copper, nickel and other metals and some of their alloys such as bronze and brass. It reacts with alkalies forming NH3.

NH4Cl + NaOH → NH3 + NaCl + H2O

Ammonium chloride decomposes to ammonia and HCl when heated. The vapor resulting from sublimation consists of equal volume of NH3 and HCl, and does not consist of molecular NH4Cl. (Young, R. D. 1976. Ammonium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd. ed. Vol. 2, p. 52l. New York: Wiley Interscience.) Reacts with formaldehyde (neutralized with NaOH) forming examethylenetetramine
and HCl.

NH4Cl + 6 HCHO → C6H12N4 + 4HCl + 6H2O

Reaction with copper(II) chloride at 2:1 ratio produces yellow orthorhombic crystals of cupric ammonium chloride, which reacts with water to form blue dihydrate crystal, ammonium tetrachlorodiaquocuprate(II): heat 2NH4Cl + CuCl2 –––→ (NH4)2 + CuCl4 evaporation A similar complex formation occurs with mercuric chloride, zinc chloride, osmium chloride and platinum (II) and (VI) chlorides, forming mercuric ammonium chloride, (NH4)2•HgCl4, zinc ammonium chloride (NH4)3ZnCl4 or ZnCl2•3NH4Cl, osmium ammonium chloride, (NH4)2OsCl6, platinum ammonium chloride, (NH4)2PtCl4 and platinic ammonium chloride (NH4)2PtCl6, respectively. Similarly, it reacts with palladium chloride to form ammonium chloropalladate, (NH4)2PdCl4. It precipitates out ammonium platinichloride from solution of chloroplatinic acid (Archibald, E. H. 1920. J. Chem. Soc., 117, 1105):

H2PtCl6 + 2NH4Cl → (NH4)2PtCl6 + 2HCl

Neutralization reaction occurs with amide, forming chloride salt and ammonia:

NH4Cl + KNH2 → KCl + 2NH3

Heating with zirconium chloride gives a tetraamine adduct:

4NH4Cl+ZrCl4ZrCl4.4NH3+4HCl

Chemical Analysis

Elemental composition: Cl 66.28%, H 7.54%, N 26.18% Ammonium chloride is analyzed by treatment with formaldehyde (neutralized with NaOH) and the product HCl formed is analyzed by titration using an acid-base color indicator such as phenolphthalein. Alternatively, it may be mixed with caustic soda solution and distilled. The distillate may be analyzed for NH3 by titration with H2SO4; or by colorimetric Nesslerization; or with an ammonia-selective electrode (APHA, AWWA, WEF. 1995. Standard Methods for the Examination of Water and Wastewater. 19th ed. Washington, DC, American Public Health Association). The presence of ammonia or any other ammonium compound would interfere in the test. The moisture content in NH4Cl may be determined by Karl–Fischer method.