Wednesday, February 6, 2013

Aqua Regia and trick of gold polishing

                                       Aqua Regia and trick of gold polishing

Aqua Regia
or Nitro-Hydrochloric acid is a highly corrosive mixure of acids , a fuming yellow or red solution . The mixure is formed by freshly mixing concentrated nitric acid and hydrochloric acid , usually in the volume ratio of 1 : 3 .
It has got its name of King's water ( Aqua Regia ) , because it can dissolve the so called noble metals , gold and platinum. Aqua regia itself is very corrosive and has been implicated in several explosions due to mishandling .
Sometimes we may have seen an old gold ornament at home that has got spots. Our parents may take it to a polisher to get it cleaned and polished . Gold in ornaments or jewellary is actually alloyed with copper or silver  , which tarnish over time.
Aqua regia is very powerful and can dissolve gold within minutes. We should not clean gold ornaments with aqua regia.  What these polishers are doing is they dip the gold ornaments in aqua regia for a little while , rinse them with water and give the ornaments back to us. Now , the gold looks new and also polished ! But in truth , aqua regia has actually eaten up few top layers of the gold.
It is so thin that we dont notice. A polisher in the name of polishing gold ornaments , he may have polished hundreds of gold ornaments. 
With this trick , he may have removed quite a few gram of gold. He can then precipitate this gold using sodium bicarbonate. But to clean gold jewellary , all we need is just soap water . Since with soap water , we can get rid of dirt on jewellary.
This is the true story of gold polishing. 

No comments:

Post a Comment