CBSE Class 10 Answered

Assertion- Silver articles become coated with a black layer upon exposure to air. Resaon- A layer of oxide gets deposited upon oxidation with air. A- Assertion and Reason both are correct and reason is the correct explanation of assertion. B- Assertion and Reason both are correct and reason is not the correct explanation of assertion. C- Assertion is true but reason is false. D- Reason is true but assertion is false Please provide an explanation too. Asked by vandanawasan02 | 13th Feb, 2020, 09:24: AM Expert Answer: Aseertion and reason both are correct and reason is correct explanation of assertion. When silver is exposed to air, it becomes black due to oxide coating, although silver is not very reactive metal but with passage of time, it slowly reacts with oxygen in the air and forms black coloures silver oxide. Follow up question- Silver forms sulphide layer upon oxidation. I am confused between B and C. A option is definitely wrong.

Asked by vandanawasan02 | 13 Feb, 2020, 02:08: PM

Expert Answer

Silver also forms Silver Sulphide because of reaction in between traces of H₂S present in environment. Silver reacts with oxygen and forms Silver Oxide. Silver Sulphide is formed in more quantity as compared to Silver oxide because Silver has more affinity to form a bond with S as compared to O. Ag reacts very slow with O.

2 A g plus O subscript 2 space space end subscript rightwards arrow A g subscript 2 O 4 A g plus 2 H subscript 2 S plus 2 O subscript 2 rightwards arrow 2 A g subscript 2 S space plus 2 H subscript 2 O

So Oxide is deposited but colour of Ag₂O is brown in layer and colour of Ag₂S is black.

So Silver is oxidised and forms Silver sulphide and Silver oxide. But black colour of layer is formed due to sulphide formation (due to high affinity with silver) which forms when silver is exposed to air.

Answered by Ravi | 13 Feb, 2020, 03:18: PM