Question

Give reason why Taj Mahal is turning yellow.

Answer 1

Reason:

• Taj Mahal consists of white marble [calcium carbonate (${\mathrm{CaCO}}_3$)].
• Air contains many gases such as nitrogen(${\mathrm{N}}_2$), oxygen(${\mathrm{O}}_2$), carbon dioxide(${\mathrm{CO}}_2$), etc.
• When the amount of these gases increases due to increasing emissions from industries and factories gases like carbon dioxide(${\mathrm{CO}}_2$), sulphur oxides(${\mathrm{SO}}_2$) and nitrogen oxides(${\mathrm{NO}}_2$) increases, causing air pollution.
• The main cause of the yellow colour of the Taj Mahal is sulphur dioxide.
• Sulphur dioxide(${\mathrm{SO}}_2$) reacts with the water molecules present in the atmosphere forming sulphurous acid(${\mathrm{H}}_2{\mathrm{SO}}_3$) and sulphuric acid(${\mathrm{H}}_2{\mathrm{SO}}_4$).
• These acids form a precipitate in the form of acid rain.

$\underset{\left(\mathrm{sulphur}\right)}{\mathrm{S}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{oxygen}\right)}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{(\mathrm{sulphur}\mathrm{dioxide})}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}$

$\underset{}{\underset{(\mathrm{sulphuric}\mathrm{acid})}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}}+\underset{\left(\mathrm{water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{sulphuric}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{SO}}_3\left(\mathrm{l}\right)}$

$\underset{(\mathrm{sulphuric}\mathrm{trioxide})}{{\mathrm{SO}}_3\left(\mathrm{l}\right)}+\underset{\left(\mathrm{water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{(\mathrm{sulphuric}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)}$

The acid rain destroys the outer layer of the Taj Mahal thus changing its colour from white to yellow due to corrosion of marble. It also makes cracks in the monument.

$\underset{(\mathrm{calcium}\mathrm{carbonate})}{{\mathrm{CaCO}}_3}+\underset{(\mathrm{sulphuric}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{l}\right)}\to \underset{(\mathrm{calcium}\mathrm{sulphate})}{{\mathrm{CaSO}}_4\left(\mathrm{s}\right)}+\underset{(\mathrm{carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Hence, the Taj Mahal is turning yellow mainly due to these reasons: air pollution, discolouration of marble due to oxidation of its constituents, environmental neglect and wear and tear caused by millions of tourists who visit it every year.