A man went door-to-door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument, the man beat a hasty repeat. Can you play the detective to find out the nature of the solution he has used?

AcademicChemistryNCERTClass 10

The dishonest goldsmith dipped the gold bangles in aqua-regia (which contains 1 part of concentrated nitric acid and 3 parts of concentrated hydrochloric acid, by volume). Aqua-regia dissolved a considerable amount of gold from gold bangles and hence reduced their weight drastically. The dishonest goldsmith can recover the dissolved gold from aqua-regia by suitable treatment. 

Extra information: Aqua regia is a mixture of Nitric and Hydrochloric acid in the ratio of 1:3, is used for the dissolution of gold. A freshly prepared aqua regia is colourless, but it turns yellow, orange or red within seconds due to the formation of nitrosyl chloride and nitrogen dioxide.

HNO3 + 3 HCl → NOCl + Cl2 + 2 H2O.

Gold is an unreactive metal. Therefore, they do not corrode easily and do not react with atmospheric air, water vapour and other gases. This is why gold looks new even after several years.]

raja
Updated on 10-Oct-2022 12:46:59

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