Question

Name the substance of black layer.

Answer 1

Hint : The substance which forms the black layer must be formed by some type of reaction. This layer may be formed by heating or by the contact with air . We will study copper oxide which is black layer substance .

Complete step by step answer
The colour of Copper is reddish brown . But when copper is heated a black layer of substance forms . This black layer substance is copper oxide .
 $ 2Cu + {O_2} \to 2CuO $
This reaction occur at the range of $ 300 - {800^ \circ }C $
Copper oxide is considered as a starting product for production of other copper salts . copper has two types of oxides which are cupric oxide $ \left( {CuO} \right) $ and cuprous oxide $ \left( {C{u_2}O} \right) $ . These two oxides are formed because of the valence shell electrons present in the copper . copper is in high demand due to its good properties .
Copper and copper oxide are used in making coins , electrical cables . Copper oxide has anti – microbial properties due to which it is also in high demand.

Additional information :
Harmful effects of copper is if its oxides are swallowed then it may cause vomiting and nausea. If copper oxide is inhaled In high doses by some means then it may cause bad effects on the lungs . Copper oxides are skin irritants too, so while handling copper oxides in the lab one needs to be very careful.
Copper when taken in a balanced form does not cause any problem, as the human body has an essential trace of copper in the immune system , skins ,formation of capillaries and heart.

Note
Just like copper which turns black when exposed to heat, silver also turns black when exposed to air .The silver reacts with the hydrogen sulphide present in the air and turns black .This occurs due to the formation of silver sulphide .