CBSE Class 10 Science 2019 · Paper 31/1/2/C · Question 6
(a) Silver articles generally turn black when kept in the open for a few days. The articles when rubbed with tooth-paste again start shining.
- (i)Why do silver articles turn black when kept in the open for a few days ? Name the phenomenon involved.
- (ii)Name the black substance formed and give its chemical formula. (b) Write the formulae of (i) calcium phosphate and (ii) ammonium carbonate.
Answer
Silver tarnishes (corrosion) to black silver sulphide, ; calcium phosphate is and ammonium carbonate .
(a)(i) Silver reacts with sulphur compounds, such as hydrogen sulphide, present in the air and forms a thin black coating of silver sulphide on its surface: . The phenomenon is corrosion (tarnishing of silver).
(a)(ii) The black substance is silver sulphide, .
(b)(i) Calcium phosphate: ; (ii) Ammonium carbonate: .
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