Question

A copper plate was dipped into a solution of silver nitrate after sometime a black layer was deposited on the copper plate why ?​

Answer 1

Black layer was deposited due to the coating of silver because copper being more reactive than silver, displaced silver from silver nitrate solution.

2AgNO3(aq)+Cu → Cu(NO3)2(aq)+2Ag(S)

Answer 2

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Copper lies above silver in the reactivity series. This means that copper is more reactive than silver. Therefore, copper had replaced silver from silver nitrate solution. Silver got deposited on the copper plate and changed to black after sometime because silver and also some salts of silver are sensitive to light. They readily become blackish on standing for on exposure to air.

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$Cu(s) + 2AgNO_3(aq) ----> Cu(NO_3)_2(aq) + 2Ag(s)$