AMMONIUM BICARBONATE
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.
Tags: AMMONIUM, AMMONIUM BICARBONATE, BICARBONATE, NH4HCO3; MW 79.06
