Ammonium Bicarbonate

Ammonium bicarbonate is a white crystalline compound with a characteristic ammonia-like odour. This water-soluble inorganic chemical is produced through the dry distillation or burning of creatine-containing substances.

Ammonium bicarbonate is a source of ammonia and is widely used in fertiliser. Additionally, it acts as a leavening agent in the production of crackers and cookies.

1.0Introduction  

Ammonium bicarbonate is a mildly basic inorganic compound composed of ammonium cations and bicarbonate anions, with the chemical formula NH₄HCO₃. It is a white crystalline solid with a strong ammonia-like odour. The compound dissolves easily in water, forming a mildly alkaline solution, but is insoluble in most organic solvents.

2.0Structure of Ammonium Bicarbonate

Ammonium bicarbonate is a colourless, crystalline solid with several alternate names, including bicarbonate of ammonia, hartshorn, AmBic, and powdered baking ammonia.

Its chemical structure comprises the ammonium cation (NH₄⁺) and the bicarbonate anion (HCO₃⁻). This mildly essential inorganic compound features molecules held together by ionic bonds.

In the structure of ammonium bicarbonate, one carbon atom is bonded to three oxygen atoms, and one of these oxygen atoms forms a bond with the ammonium ion.

Ammonium bicarbonate is thermally unstable and begins to decompose at temperatures above 35°C.

3.0Production of Ammonium bicarbonate 

Ammonium bicarbonate (NH₄HCO₃) is synthesised by reacting carbon dioxide (CO₂) with ammonia (NH₃) in the presence of water. The reaction is conducted under very low temperatures to prevent the thermal instability of ammonium bicarbonate, which decomposes at moderately elevated temperatures.

Reaction:

CO₂+NH₃+H₂O→NH₄HCO₃

The process begins by passing ammonia gas through a concentrated aqueous solution of sodium sesquicarbonate, which is a mixture of ammonium bicarbonate (NH₄HCO₃), ammonium carbonate (NH₄)2CO₃​, and water. The ammonia reacts with the solution to form ammonium carbonate.

At around 30°C, ammonium carbonate crystallises from the solution. However, ammonium carbonate is unstable in air and decomposes into ammonia (NH₃) and ammonium bicarbonate (NH₄HCO₃), as shown in the decomposition reaction:

(NH₄)₂CO₃→2 NH₃+NH₄HCO₃

This decomposition highlights the thermal instability of ammonium carbonate, which is why the reaction to stabilise ammonium bicarbonate is carried out at low temperatures.

4.0Physical Properties of Ammonium Bicarbonate 

• Appearance: White crystalline solid.
• Density: 1.59 g/mL.
• Decomposition Temperature: 41.9°C.
• Odour: Strong ammonia-like aroma with a pungent smell.
• Solubility: Highly soluble in water.

5.0Chemical Properties of Ammonium Bicarbonate

• Solubility: Ammonium bicarbonate is insoluble in most common organic solvents such as benzene, ethanol, alcohol, ketones, and acetone.
• Endothermic Decomposition: When heated, ammonium bicarbonate undergoes an endothermic reaction, absorbing energy and decomposing into ammonia, carbon dioxide, and water.

NH₄HCO₃→NH₃+CO₂+H₂O

• Reaction with Acids: Ammonium bicarbonate reacts with acids to form ammonium salts, releasing carbon dioxide and water. For example, when it reacts with hydrochloric acid (HCl):

NH₄HCO₃+HCl→NH₄Cl+CO₂+H₂O

• Reaction with Bases: Ammonium bicarbonate reacts with bases to release ammonia gas.
• Dissolution in Water: Ammonium bicarbonate dissolves in water to form a mildly alkaline solution.

6.0Reactions of Ammonium Bicarbonate

1. Reaction with Sulfates: When ammonium bicarbonate reacts with the sulfates of alkaline earth metals, metal carbonates are precipitated. For example:

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

2. Reaction with Metal Halides: Ammonium bicarbonate reacts with metal halides from alkali metals to form bicarbonates and ammonium halides. For example:

• NH₄HCO₃+NaCl→NH₄Cl+NaHCO₃
• NH₄HCO₃+KI→NH₄I+KHCO₃
• NH₄HCO₃+NaBr→NH₄Br+NaHCO₃

7.0Applications of Ammonium Bicarbonate

• Leavening Agent: Before baking powder was invented, this agent was used in baking cookies and crackers, replacing yeast or baking powder.
• Research and Industry: Used as a reagent in labs and industrial processes.
• Protein Analysis: Helps in protein analysis using mass spectrometry.
• Ammonium Salt Production: Used in making ammonium salts for various industries.
• Fertilizer: Provides nitrogen to support crop growth.
• Fire Extinguishers: These are used in fire extinguishers due to their chemical properties.
• Dyes and Pigments: Involved in producing dyes and pigments.
• Paints and Pharmaceuticals: These are used to produce paints and medicines.
• Plastic and Rubber: Raw material for foamed plastics in these industries.
• Ceramics and Leather: Used in ceramics and leather tanning.
• Liquid Chromatography: Adjusts pH in chromatography solutions.
• Medicinal Products: Found in cough syrups and other medicines.