Question

Give Reasons:
a. Silver and copper turn green over time.

Answer 1

Actually, Silver articles turn black and copper turns green after sometimes

WHY?

Black colour of silver is due to the formation of AgS and green colour on copper items is due to the formation of CuCO3

This is because these metals are attacked by moisture, CO2, H2S and acids etc. present in the atmosphere.

So they corrode and their color changes

Answer 2

Answer: Copper turns green as it reacts with to form (Patina). A flaky layer is obtained when we scratch the surface. It is basic copper carbonate.

$\rm Cu \ (s) + CO_2 \ (g) + \ O_2 \ (g) + H_2O \ (g) \rightarrow CuCO_3 . Cu(OH)_2 \ (s)$

More: Silven doesn't turn green. It turns black as it reacts with hydrogen sulphide to from silver sulphide. It is called tarnishing of silver. Corroded silver = $\rm Ag_2S$.