Gold element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides). Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of nitric acid and hydrochloric acid, which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic objects, giving rise to the term "acid test". Gold also dissolves in alkaline solutions of cyanide,
Acid-base extraction Acid-base extraction Acid-base extraction is a procedure using sequential liquid–liquid extractions to purify acids and bases from mixtures based on their chemical properties. Acid-base extraction is routinely performed during the work-up after chemical syntheses and for the isolation of compounds and natural products like alkaloids from crude extracts. The product is largely free of neutral and acidic or basic impurities. It is not possible to separate chemically similar acids or bases using this simple method. The fundamental theory behind this technique is that salts, which are ionic, tend to be water-soluble while neutral molecules tend not to be. The addition