Question

The colour of Copper oxide is
(a). Black
(b). Blue
(c). Brown
(d). Green

Answer 1

Hint: The molecule given in the question is widely used as a pigment to colour ceramics, artificial gems, porcelain glazes, enamels etc. Not only this, it is also used in the manufacture of phosphors (materials that glow in dark after they are exposed to light).

Complete step-by-step solution -

Copper is a d-block element with an atomic number - 29 and an electronic configuration - \[[Ar]3{{d}^{10}}4{{s}^{1}}\].
Copper (metal) turns black when it is heated. It is because heated copper reacts with oxygen to form copper oxide, which is black in colour. The reaction is as follows –
\[2Cu(s)+{{O}_{2}}(g)\to 2CuO(s)\]
Cupric Oxide is a black metallic oxide present in solid state, soluble in dilute acids and ammonium hydroxide but insoluble in water and organic solvents. It is not only used as a pigment, but also as an insecticide, fumigant, wood preservative, welding flux, antifouling agent, in manufacture of phosphors, etc.
Therefore, the answer is option (a) – Black.

Additional Information:
Copper(I) Oxide is also known as Cuprous Oxide and Copper (II) Oxide is known as Cupric Oxide. Also, if we need to obtain the original copper colour, we can place the metal in a hydrogen atmosphere. The following reaction takes place -
\[CuO(s)+{{H}_{2}}(g)\to Cu(s)+{{H}_{2}}O(g)\]

Note: Do not get confused between Copper(I) Oxide and Copper (II) Oxide. Copper (I) oxide is red in colour. Since red is not given in the options, we know for sure that it cannot be Copper (I) Oxide. Copper shows these colours because of the d-d transitions, i.e. when electrons absorb energy, they excite and jump to a higher energy level. But, electrons are not stable at higher energy levels, so it comes back to its orbital by releasing energy in the wavelength of the visible spectrum.