Metals such as gold and silver are known to be unreactive to both \(HCl\) and \(HNO_3\). On the other hand, the combination of these two acids will dissolve gold. This mixture is called aquaregia.
It is a \(3:1\) combination of hydrochloric acid and nitric acid that has been properly prepared. It's a fuming yellow-orange liquid, It is a highly corrosive liquid that can attack gold and other resistant substances. The chemical formula of aquaregia is \(3\)\(HCl+HNO_3\). It is miscible in water.
Aquaregia is a Latin word that means "King's Water". The name reflects the ability of aquaregia to dissolve noble metals such as gold, platinum and palladium.
Uses of aquaregia:
  • The most common application of aquaregia is in the Wohlwil process, which is used to refine gold. During this process, we obtain high purity gold (\(99.999%\)).
  • It is used in the itching of various metals.
  • It is also used to remove metals like gold and platinum.
Already we have studied that in an aqueous solution, an acid can produce hydrogen ions (\(H^+\)), while a base can produce hydroxyl ions (\(OH^-\)). When an acid and a base react, a neutral product is formed, which is called salt.
According to Arrhenius theory, bases are substances that ionise in water to form hydroxyl ions (\(OH^-\)).
Some metal oxides give salt and water on reaction with acids. These are also called bases. Bases that are soluble in water are called alkalis.
When a base reacts with water, salt and water are produced.
Bases contain one or more replaceable oxide or hydroxyl ions in solution.
All alkalis are bases, but not all bases are alkalis. For example \(NaOH\) and \(KOH\) are alkalis, whereas \(Al(OH)_3\) and \(Zn(OH)_2\) are bases.