What makes Koenigswasser so strong

Aqua regia

English: aqua regia

1 definition

Aqua regia is a mixture of hydrochloric and nitric acid in a ratio of 3: 1. It has such a high oxidizing power that it can even dissolve the precious metals gold and platinum.

2 background

The dissolution process corresponds to an oxidation reaction. Whether a metal goes into solution depends on the electrochemical potential. Noble metals such as gold or platinum have a positive potential and are therefore difficult to oxidize. For this reason, strong oxidizing agents are needed to dissolve precious metals.

3 effect

When nitric acid and hydrochloric acid are mixed together, nascent chlorine and nitrosyl chloride are created - both chemicals whose oxidizing power is strong enough to dissolve gold and platinum. Silver, on the other hand, is not dissolved because a passivating silver chloride layer is formed. Another mode of action is based on the complexation of noble metal ions. This reduces their concentration in the solution, which lowers the redox potential and makes the noble metal easier to oxidize.

A combination of both modes of action is also possible.[1]

4 application

Aqua regia is mainly used in qualitative analysis to bring poorly soluble substances into solution (aqua regia digestion). In the Wohlwill process, aqua regia is used to purify gold.[2]

5 sources

  1. ↑ Riedel, Erwin; Janiak, Christian: Inorganic Chemistry, De Gruyter, 9th edition, 2015
  2. ^ Mark Anthony Benvenuto: Metals and Alloys: Industrial Applications, De Gruyter, 2016