Ammonium bicarbonate

Overview

Ammonium bicarbonate, also called bicarbonate of ammonia, ammonium hydrogen carbonate, hartshorn, or powdered baking ammonia, is the bicarbonate salt of ammonia.

Ammonium bicarbonate is formed as shown below, or by passing carbon dioxide through a solution of the normal compound, when it is deposited as a white powder, which has no smell and is only slightly soluble in water. The aqueous solution of this salt liberates carbon dioxide on exposure to air or on heating, and becomes alkaline in reaction. The aqueous solutions of all the carbonates when boiled undergo decomposition with liberation of carbon dioxide and the substance with which the carbonate ion reacted to form the bicarbonate, in this case, ammonia:

NH₄HCO₃ → NH₃ + H₂O + CO₂

Properties

At room temperature ammonium bicarbonate is a white, crystalline powder with a slight odour of ammonia that can dissolve in water to give a mildly alkaline solution. It is however insoluble in acetone and alcohols. Ammonium bicarbonate decomposes at 36 to 60 °C into ammonia, carbon dioxide and water vapor in an endothermic process (as it is with many ammonium salts) and so causes a drop in the temperature of the water. When reacted with acids carbon dioxide is produced, while reactions with alkalis give ammonia.

Uses

Ammonium bicarbonate was used in the food industry as a raising agent (e.g., for gingerbread or Chinese youtiao) before the introduction of baking soda. Ammonium bicarbonate is still used in many food products, in addition to baking soda. Many baking cookbooks (especially from Scandinavian countries) may still refer to it as hartshorn or hornsalt . It is fine to replace it with baking soda.

It is commonly used as an inexpensive nitrogen fertilizer in China, but is now being phased out in favor of urea because of its relatively low quality and instability. This compound is used as a component in the production of fire-extinguishing compounds, pharmaceuticals, dyes, pigments and it is also a basic fertilizer being a source of ammonia. Ammonium bicarbonate is still widely used in the plastic and rubber industry, in the manufacture of ceramics, in chrome leather tanning and for the synthesis of catalysts.

Safety

Ammonium bicarbonate is an irritant to the skin, eyes and respiratory system. Additionally, the acrylamide that is formed during the baking process has been connected to cancer in lab animals.

See also

• Ammonium carbonate