Gold with hydrofluoric, hydrochloric, hydrobromic, hydriodic, sulfuric, or nitric acid. It does react with selenic acid, and is dissolved by aqua regia, a 1:3 mixture of nitric acid and hydrochloric acid. Nitric acid oxidizes the metal to +3 ions, but only in minute amounts, typically undetectable in the pure acid because of the chemical equilibrium of the reaction. However, the ions are removed from the equilibrium by hydrochloric acid, forming AuCl ions, or chloroauric acid, thereby enabling further oxidation. Gold is similarly unaffected by most bases. It does not react with aqueous, solid, or molten sodium or potassium hydroxide. It does
Chromotropic acid Chromotropic acid Chromotropic acid has the formula is (HO)CH(SOH). It can be used for as a reagent in the quantitative determination of the systemic herbicide, 2,4-dichlorophenoxyacetic acid. Chromotropic acid is also used for testing of presence of formaldehyde. The usefulness of this reagent in quantitative determination is the formation of a red colouration (peaking at 580 nm wavelength) when chromotropic acid in 50% sulfuric acid reacts with formaldehyde. The colouration is specific to this aldehyde and is not produced from other organic species such as ketones and carboxylic acids. The NIOSH Formaldehyde method #3500 is the reference analytical standard that