Nitric acid with gold

J. Tafel found that while nitric acid is reduced only to hydroxylamine q.v.) by mercury or well-amalgamated electrodes, a copper cathode reduces it to ammonia and at the same time has no action on hydroxylamine. A. Brochet and J. Petit studied the electro-reduction of nitric acid by an alternating current. T. H. Jeffery described the electrolysis of nitric acid with a gold anode, and obtained from the anode liquor crystals of aurinitric acid, HAu(N03)4.3H20. R. Ihle s observations on the oxidation-potential of nitric acid have been discussed in connection with nitrous acid (q.v.). He found that if the cone, of the nitric acid be expressed by... 

The process of assaying gold was current from early times and in the thirteenth century it was clearly described in the Summaperfectionis magisterii (ascribed to Geber). This also described the preparation of aqua fortis (nitric acid), which was known to dissolve silver but not gold, and aqua regia, prepared from a mixture of nitric acid with ammonium chloride, which... 

Many of the early studies on gold arose from alchemy, in which people attempted to turn cheap metals, such as lead, into gold. Alchemists discovered that gold can be dissolved in a 3 I mixture of concentrated hydrochloric and nitric acids, known as aqua regia ( royal vrater ). The action of the nitric acid on gold is similar to that on copper (Equation 4.31) in that the nitrate ion, rather than H, oxidizes the metal to Au . The Cl ions interact with Au " to form highly stable AuCl4 ions. The net ionic equation is... 

Nitric acid reacts with all metals except gold, iridium, platinum, rhodium, tantalum, titanium, and certain alloys. It reacts violentiy with sodium and potassium to produce nitrogen. Most metals are converted iato nitrates arsenic, antimony, and tin form oxides. Chrome, iron, and aluminum readily dissolve ia dilute nitric acid but with concentrated acid form a metal oxide layer that passivates the metal, ie, prevents further reaction. 

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