Which one of the following acid is used by goldsmith for cleaning of gold and silver articles?
- A.Sulphuric acid
- B.Nitric acid
- C.Hydrochloric acid
- D.Phosphoric acid
Correct answer
Explanation
The correct answer is B, Nitric acid. Goldsmiths dip gold and silver ornaments in dilute nitric acid to dissolve the dirt, oxide layers and traces of base metals stuck to them, which brings back their shine.
Gold does not react with nitric acid alone, which is why the acid can clean it safely and why it is also used in the traditional "acid test" for gold: base metals and imitation jewellery are attacked, while real gold is not. Gold dissolves only in aqua regia, a 3:1 mixture of concentrated hydrochloric acid and nitric acid. Nitric acid is also used to make fertilizers such as ammonium nitrate and explosives such as TNT.
A is wrong because sulphuric acid is used in car batteries and fertilizer making, not for cleaning ornaments.
C is wrong because hydrochloric acid on its own is not the goldsmith's cleaning acid; it is used to clean iron before galvanising.
D is wrong because phosphoric acid is used in fertilizers and soft drinks.
Exam tip: goldsmith's acid = nitric acid; aqua regia (3 HCl : 1 HNO₃) dissolves gold and platinum.
Practice Questions
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- C.has high chemical stability
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- A.Cavity of tooth
- B.Erosion of nail
- C.Deformation of bone
- D.Mottling of tooth
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- A.1 and 3 only
- B.2 and 3 only
- C.1 and 2 only
- D.1, 2 and 3
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- C.Gibberellin
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- A.Phosphorus
- B.Carbon
- C.Oxygen
- D.Nitrogen
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