Silver artefacts get tarnished in air due to the formation of
- A.silver chloride
- B.silver oxide
- C.silver sulphide
- D.silver sulphate
Correct answer
Explanation
The correct answer is C, silver sulphide. Silver turns black in air because it reacts with sulphur compounds, mainly hydrogen sulphide, to form a thin black coating of silver sulphide (Ag₂S).
Silver is a noble metal and hardly reacts with oxygen at room temperature. But air, especially in towns and kitchens, carries traces of hydrogen sulphide from decaying matter, fuels and foods such as eggs. These react with the silver surface: 4Ag + 2H₂S + O₂ → 2Ag₂S + 2H₂O. The black layer is this tarnish, and it can be removed by gentle polishing or by placing the article in hot baking soda solution in an aluminium pan.
A is wrong because silver chloride forms with chlorine or chlorides and is white, turning grey in light.
B is wrong because silver does not readily oxidise in air at ordinary temperatures.
D is wrong because silver sulphate is a white salt made with sulphuric acid, not a tarnish.
Exam tip: silver blackens (Ag₂S), copper turns green (basic copper carbonate), iron rusts (hydrated iron oxide).
Practice Questions
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- D.Endoplasmic reticulum
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- D.Potato, garlic, turnip
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- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
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- A.equal to its weight.
- B.less than its weight.
- C.greater than its weight.
- D.zero.
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