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Q89
(NDA-II/2023)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
Official Key
Which one of the following acid is used by goldsmith for cleaning of gold and silver articles ?
Result
Your answer:
—
·
Correct:
B
Explanation
Goldsmiths primarily use Nitric acid (HNO₃) for the cleaning and purification of gold and silver articles. It is a strong oxidizing acid that effectively dissolves base metal impurities like copper, zinc, and lead from gold alloys without dissolving the gold itself.
- Gold Refining: In a process known as 'parting', nitric acid is used to separate silver and other impurities from gold, as gold remains insoluble in pure nitric acid.
- Cleaning: It is used to remove surface oxidation and tarnish from silver and gold ornaments, restoring their luster.
- Aqua Regia: While a mixture of nitric acid and hydrochloric acid (Aqua Regia) can dissolve gold, pure nitric acid is the standard choice for removing non-gold metallic contaminants.
Other acids like sulphuric acid are sometimes used for 'pickling' to remove flux after soldering, but nitric acid remains the primary chemical for deep cleaning and refining in jewelry making.
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