Question

A shiny brown colored element “X” on heating in air becomes black in color. Can you predict the element X and the black colored substance formed? How do you support your predictions?

Answer 1

Hint – In this question use the fact that copper is a shiny brown element and it is readily combustible. When it burns in air or in other words when it reacts with oxygen and is subjected to heat it results in formation of cupric oxide that is (CuO ). Think about the color of cupric oxide. This approach will help get the answer to this problem statement.

Complete answer:-
As we know that copper (Cu) reacts with oxygen ($O_2$) (I.e. heating in air as in air there is oxygen) gives us cupric oxide (CuO).
The chemical reaction is shown below,
Here we use 2 units of copper and one unit of oxygen.
$ \Rightarrow 2Cu\left( {{\text{brown}}} \right) + {O_2}\left( {{\text{air}}} \right)\xrightarrow{{{\text{heating}}}}2CuO\left( {{\text{black}}} \right)$
Now as we see copper is in brown color and cupric oxide is in black color.
Therefore shinny brown colored element X is copper and the black colored substance formed is cupric oxide.
So this is the required answer.

Note – In actual copper is red-orange colored and is considered to be of brown color. If we talk about the light intensity spectrum of copper, when light is shined upon copper metal, the copper atoms absorb some of the light in blue-green region in the spectrum, now when this blue-green light is absorbed by copper than the complimentary color that is red-orange is reflected and it held accountability for the color of copper.