Question

One gas bleaches the colour of flowers by reduction and another gas by oxidation. What are these gases?

Answer 1

• Coloured pigments present in the flowers can be decolourized by bleaching them. Bleaching of the coloured pigment can be done by oxidizing and reducing the coloured pigment.
• The gas which bleaches the colour of the flower by reduction is ${\mathrm{SO}}_2$. It reacts with moisture to produce hydrogen, Hydrogen thus produced combines with the coloured pigment to reduce them.

${\mathrm{SO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

• The gas which bleaches the colour of a flower by oxidation is ${\mathrm{Cl}}_2$. It reacts with moisture to produce oxygen, oxygen thus produced combines with coloured pigment to oxidize them.

$2{\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 4\mathrm{HCl}\left(\mathrm{aq}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$