Question

On adding dil $ HCl $ to copper oxide powder, the solution formed is blue green. Predict the new compound formed which imparts a blue green colour to solution.

Answer 1

Hint: Copper is the second last member of $ 3d - series $ transition metal. It belongs to the d-block elements. It is called a transition metal because in the $ + 2 $ oxidation state only it does not contain $ {d^{10}} $ configuration. Thus show specific properties of transition metal.

Complete step by step solution
Copper belongs to the $ 3d - series $ transition metals. The electronic configuration of copper with atomic number $ 29 $ will be- $ 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1}3{d^{10}} $ . This is an exceptional configuration as to completely fill the d orbital one electron from s orbital moves to the d orbital and has a fully filled stable configuration.
As we know transition metals have very special and unique properties, imparting colour in the salts is also a necessary property.
The d block elements have electrons in the d-subshell. Hence when the electrons are subjected to absorb energy they transmit the extra energy which in further gives the compound a good colour.
We know that copper mostly exists in two oxidation states which are $ + 1 $ and $ + 2 $ .
The colour of cuprous oxide ( $ C{u_2}O $ ) where the oxidation state of copper is $ + 1 $ , was found to be red and the colour of cupric oxide ( $ CuO $ ) where the oxidation state of copper is $ + 2 $ , was found to be black.
So when we add dilute hydrochloric acid on a solution of copper oxide, the formation of copper chloride takes place. The colour of copper chloride is blue-green, so the colour of solution is also blue-green.
The reaction can be represented as-
 $ CuO(aq) + 2HCl(dil) \to CuC{l_2}(aq) + {H_2}O $
The copper chloride formed can be used in different inorganic and organic reactions as a catalyst.

Note:
Copper chloride is mostly nowadays used as a catalyst for organic and inorganic reactions. It can also be used in providing colour as mordants for dyeing and printing of textiles in many industries. It can also be added as a pigment in glass and ceramics to give colour to the materials for decorative purposes.