~SULFAMIC ACID
Sulfamic acid is a moderately strong acid, Ka = 1.01 x 10−1. Because the solid is non-hygroscopic, it is used as a standard in acidimetry (quantitative assays of acid content).
Sulfamic acid melts at 205 °C before decomposing at higher temperatures to H2O, SO3, SO2, and N2.
Water solutions are unstable and slowly hydrolyze to ammonium bisulfate, but the crystalline solid is indefinitely stable under ordinary storage conditions.
Sulfamic acid is used as an acidic cleaning agent, sometimes pure or as a component of proprietary mixtures, typically for metals and ceramics. It is frequently used for removing rust and limescale, replacing the more volatile and irritating hydrochloric acid, which is however cheaper. It is often a component of household descaling agents, for example, Lime-A-Way Thick Gel contains up to 8% sulfamic acid and pH 2 - 2.2, or detergents used for removal of limescale. When compared to most of the common strong mineral acids, Sulfamic acid has desirable water descaling properties, low volatility, low toxicity and is a water soluble solid forming soluble calcium and iron-III salts. Its also finds applications in the industrial cleaning of dairy and brew-house equipment. Although it is considered less corrosive than hydrochloric acid due to its lower pKa, corrosion inhibitors are often added to commercial cleansers of which it is a component. It is possible that the amino group could act as a ligand under certain circumstances, as does the chloride ion for Fe-III, when hydrochloric acid is used in rust removal.