Question

Complete the following table that refers to the action of heat on some carbonates:

Carbonate	Colour residue on cooling
Zinc carbonate
Lead carbonate
Copper carbonate

Answer 1

Hint: Colour of the metal carbonates results from the empty orbitals which are present in the metal, which is also the central atom of the metal carbonate.
-After the excitation of electrons from ground state to an excited state, when the solution is cooled the electrons come back to its ground state, which releases some radiation falling in the visible region. Which ultimately is the reason why some metal carbonate precipitates impart colour to the solution, upon cooling.

Complete answer:
The complete table is given below, the colour residue on cooling the precipitate of zinc carbonate is white. The colour residue of lead carbonate is yellow, when it is cooled. And the cooled colour ratio of copper sulphate turns out to be black. The three of them are neutral compounds, and differ from each other because of the central metal ion to which carbonate is attached. Generally, we know that oxidation of copper results in formation of black precipitate on its surface.

Carbonate	Colour residue on cooling
Zinc carbonate	white
Lead carbonate	yellow
Copper carbonate	black

The colour of the compounds is due to the presence of empty orbitals in the elements lead and copper. The precipitate of these elements as carbonate, when present in hot solution, the electrons attain an excited state, from the ground state. And while cooling down, the electrons come back to the ground state which releases the energy in the form of radiations, and the colour of the solution changes, as the radiations have the wavelength corresponding to the visible region of the spectrum. We all know that the spectrum consists of different regions, like that of visible region, infrared, ultraviolet region etc.
If we consider the compound zinc carbonate which is written in the first column, we can see that it has white coloured residue on cooling, this is because the zinc does not have any empty orbitals, it has fully filled orbital configuration, so it does not have room for excitation, like that of lead and copper.

Note:The precipitate of copper carbonate is black in colour, and the precipitate of zinc carbonate and lead carbonate are white and yellow in colour respectively. The colour of these compounds exists because of the presence of empty orbitals in their subshells. Zinc is an exception, this is why its precipitate is colourless or white.