8.12 How do you count for the following observations?

(b)  When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why ? 

Answers (1)

Answer(b)-

  • Concentrated sulphuric acid is added to an inorganic mixture containing chloride-

                    2NaCl\:+\:2H_{2}SO_{4}\rightarrow \: 2NaHSO_{4}\:+\: 2HCl

          HCl is a weak reducing agent and it cannot reduce H_{2}SO_{4} to SO_{2}  thats why we get colourless pungent smelling gas HCl.

  • Concentrated sulphuric acid is added to an inorganic mixture containing bromide-

                  2NaBr\:+\:2H_{2}SO_{4}\rightarrow \: 2NaHSO_{4}\:+\: 2HBr

          2HBr + H_{2}SO_{4}\:\rightarrow \:Br_{2} ( Red \:Vapour)\:+\:SO_{2}\:+\:2H_{2}O

When conc. sulphuric acid is added to an inorganic mixture containing bromide initially it produces HBr and it is a strong reducing agent so it reduces H_{2}SO_{4} to SO_{2}  with evolution of is a red vapor of bromine.

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