NH4i

NH4I, or ammonium iodide, is an inorganic salt composed of ammonium cations (NH4+) and iodide anions (I−). It is a white, crystalline solid that is highly soluble in water, where it dissociates into NH4+ and I−. In solution, the ammonium ion can hydrolyze slightly, giving a mildly acidic pH.

Preparation and occurrence

NH4I can be prepared by neutralizing hydroiodic acid (HI) with ammonia (NH3) to form NH4I and water. It can also arise in solution when ammonium salts are treated with iodide sources and conditions favoring salt formation. The compound is typically handled as a laboratory reagent or analytical standard rather than a material found naturally.

Chemical properties

In solid form, NH4I is stable at room temperature but decomposes upon heating to release ammonia (NH3) and hydrogen iodide (HI): NH4I → NH3 + HI. In aqueous solution, the iodide ion behaves as a typical halide ion and can be involved in redox chemistry in the presence of appropriate oxidants. Iodide can also participate in precipitation reactions, for example forming silver iodide when combined with silver ions under suitable conditions.

Uses

NH4I serves as a convenient source of iodide ions in chemical syntheses and analytical procedures. It is used in qualitative inorganic analysis to supply iodide for tests and as a reagent in various iodination and iodide-related applications where a soluble iodide source is required.

Safety and handling

NH4I is a salt that can irritate skin, eyes, and the respiratory tract. It should be stored in a cool, dry place away from oxidizers and acids. If heated strongly, it releases hazardous gases such as ammonia and hydrogen iodide, so appropriate ventilation and precautions are advised.