New stoichiometry for copper dissolution in nitric acid

Abstract

Although the dissolution of copper in nitric acid was the object of numerous investigations, little attention has been paid to the stoichiometry of this reaction. We have found that nitrous acid, HN02, is one of the products, and it plays an important role in the intermediate steps of copper dissolution as well.1 We also found the quantities of HN02 and NO gas produced vary from one experiment to another depending on the conditions and, thus, no definite stoichiometry could be predicted for this reaction. The explanation lies with the specific mechanism: the dissolution of copper in nitric acid takes place at first by the reduction of NO3-to HN02, then after a certain accumulation of HN02, the reduction of HN02 to NO gas at the copper surface becomes the predominant process. During these reduction stages, copper is oxidized simultaneously. The evolved NO gas was found2,3 to react with HNO3 to give HN02:

Investigation dissolution behaviours and kinetics parameters of ulexite in boric acid solution

“…The variation shape of solid products and solid/ liquid interaction can cause undesired results. [42][43][44][45][46][47] The reactions that will occur are listed below. In reactions with the excessive liquid phase, the concentration is considered to remain constant during the reaction.…”

Mechanistic Study of the Production of NOx Gases from the Reaction of Copper with Nitric Acid

“…A proper description of the dissolution process is critical to predicting and understanding the origin of the NO x products as a function of experimental conditions, such as acid concentration. This has led to some debate about the stoichiometric reactions describing the process; − however, three overall reactions are considered that give guidance to the different reaction routes for varying concentrations of HNO 3 : Reaction is expected to be the dominant process at high concentrations of acid, and reaction is the more dominant one as the acid concentration decreases. The HNO 2 product is considered to be the autocatalytic species, and as such, it is produced during the course of the reaction and is responsible for driving the rate of the reaction.…”