A chemical formula provides a concise way to represent a substance’s composition, indicating the types of atoms and their proportions. The formula (NH4)2S describes a specific chemical compound. Understanding such formulas is fundamental in chemistry for identifying and classifying materials.
Its Chemical Name
The chemical compound represented by the formula (NH4)2S is formally known as ammonium sulfide. This name is derived from its constituent ions, following established rules for naming ionic compounds.
The (NH4)+ portion is the ammonium ion, a polyatomic cation comprising one nitrogen and four hydrogen atoms, carrying a single positive charge. The S2- component is the sulfide ion, a sulfur atom that has acquired two electrons, resulting in a negative two charge.
In ionic compound nomenclature, the positively charged ion (cation) is named first, followed by the negatively charged ion (anion). To achieve electrical neutrality, two ammonium ions (each with a +1 charge) balance the -2 charge of a single sulfide ion, leading to the formula (NH4)2S. The compound is also sometimes referred to as diammonium sulfide due to the presence of two ammonium groups.
Key Properties
Ammonium sulfide typically exists as a colorless to yellowish liquid in solution, its most common commercial form. Below -18 °C, it can solidify into hygroscopic yellow crystals. A prominent characteristic is its strong, unpleasant odor, often likened to rotten eggs. This distinctive smell primarily arises from the release of hydrogen sulfide (H2S) gas, a common byproduct of its decomposition.
The compound exhibits high solubility in water, forming alkaline aqueous solutions with a pH typically ranging from 9 to 11. Ammonium sulfide is inherently unstable, particularly when exposed to air, heat, or acids. It readily decomposes at ambient temperatures, releasing both ammonia and hydrogen sulfide gases.
This decomposition is accelerated by moisture and heat, necessitating careful storage in cool, dry places away from acids and oxidizing agents to minimize hazardous gas release. Maintaining a pH of approximately 9.5 can help suppress decomposition in solutions. Due to its instability, commercial ammonium sulfide solutions often contain a mixture of ammonia and ammonium hydrosulfide, rather than pure ammonium sulfide.
Common Applications and Safety
Ammonium sulfide finds various applications. It has been historically used in analytical chemistry as a reagent for precipitating metal sulfides. In the textile industry, it is employed in dyeing processes and for applying patina to bronze. It is also utilized in photographic developers and is a primary ingredient in “stink bombs” due to its powerful, unpleasant odor.
Handling ammonium sulfide requires caution due to the potential release of hydrogen sulfide (H2S) gas. Hydrogen sulfide is a highly toxic, corrosive, and flammable gas, capable of causing severe respiratory issues and even death at high concentrations. Low concentrations can irritate the eyes and respiratory tract, while higher levels can lead to rapid unconsciousness. The compound itself is corrosive, causing burns and irritation upon direct contact with skin, eyes, and mucous membranes.
Proper ventilation is crucial when working with ammonium sulfide to prevent H2S gas buildup. Storage should occur in tightly sealed containers in a cool, well-ventilated area, away from incompatible materials like acids and strong oxidizing agents. Personal protective equipment, including chemical goggles, face shields, and chemical-resistant gloves, minimizes direct exposure.