Aqueous ammonia is a solution of ammonia gas dissolved in water, creating a clear, colorless liquid with a characteristic pungent odor. This substance is widely used in global commerce as a raw material and processing agent across numerous industries. Its utility stems from its alkaline nature and its high concentration of available nitrogen, making it common in products found in homes, farms, and industrial facilities worldwide.
Chemical Identity and Forms
Aqueous ammonia is chemically defined as a solution where gaseous ammonia (\(\text{NH}_3\)) is dissolved in water (\(\text{H}_2\text{O}\)). Although often written as ammonium hydroxide (\(\text{NH}_4\text{OH}\)), this formula represents its behavior in solution rather than its true composition. In an aqueous solution, ammonia and water are in a dynamic equilibrium, but only a small fraction of ammonia molecules react to form ammonium (\(\text{NH}_4^+\)) and hydroxide (\(\text{OH}^-\)) ions. The majority remains as dissolved \(\text{NH}_3\) molecules, which explains its strong, volatile odor.
The solution is known by several interchangeable names, including ammonia solution, aqua ammonia, ammonia water, and ammonium hydroxide. Concentration varies significantly depending on its intended use. Household cleaning products are dilute, typically 5% to 10% ammonia by weight. Industrial-grade solutions are far more concentrated, often reaching 26 degrees Baumé, corresponding to approximately 29.4% ammonia by weight.
The primary difference between the aqueous form and pure ammonia gas (anhydrous ammonia) is the presence of water. This significantly reduces the pressure and volatility of the compound. Unlike ammonia gas, which must be stored under high pressure, the dissolved form is a liquid that can be stored in less specialized containers, making it safer to handle and transport.
Widespread Commercial and Industrial Applications
Aqueous ammonia is a widely used cleaning agent, leveraging its alkalinity and volatility for effective degreasing. When applied to surfaces, the ammonia readily reacts with fats and oils, breaking them down for easy removal. The dissolved ammonia then evaporates quickly, leaving behind few streaks or residue on materials like glass and stainless steel.
The largest commercial application for aqueous ammonia is in the agricultural sector, where it serves as a source of nitrogen for plant nutrition. It is applied directly to soil as a liquid fertilizer (aqua ammonia), or used as a chemical precursor in the manufacture of solid nitrogen-based fertilizers. These solid forms include compounds like urea and ammonium nitrate, which maximize crop yields globally.
Industrial processes rely on this chemical for its ability to adjust and maintain \(\text{pH}\) levels. In water treatment facilities, aqueous ammonia is used to neutralize acidic waste streams and control the \(\text{pH}\) of water supplies. It is also combined with chlorine to form chloramines, which are used as a longer-lasting disinfectant in municipal water distribution systems.
The textile industry employs aqueous ammonia in various stages of fabric processing, using its chemical properties to prepare materials for dyeing and finishing. It is used in pre-treatment steps, such as scouring cotton fibers to remove natural waxes and oils, or degumming raw silk to remove the sericin coating. It is also used in industrial systems designed to reduce atmospheric pollution, specifically in Selective Catalytic Reduction (SCR) systems to neutralize nitrogen oxide (\(\text{NO}_{\text{x}}\)) emissions from large combustion sources.
Safe Handling and Practical Precautions
Handling aqueous ammonia requires adherence to safety protocols due to the irritating and corrosive nature of the solution and its vapors. Adequate ventilation is necessary whenever the product is used, even in household applications, because the ammonia readily off-gasses. Inhaling the concentrated fumes can cause severe irritation to the eyes, nose, throat, and lungs.
Never mix aqueous ammonia, or any product containing it, with chlorine bleach. This combination triggers a chemical reaction that generates chloramine gas, a respiratory irritant that can cause serious lung damage and potentially lead to death. This danger exists even when mixing small amounts of common household cleaners containing these ingredients.
Proper storage is necessary to minimize exposure and maintain product integrity. The solution should be kept in a tightly sealed container and stored in a cool, dry, and well-ventilated location, away from direct sunlight, heat sources, and incompatible materials, especially strong acids. Because the solution is corrosive and can cause chemical burns upon contact, protective measures like gloves and eye protection are recommended during handling.