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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 the colourless,  pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why ? 

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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}  that's why we get the 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}  is a red vapour of bromine with evolution.

Posted by

Gautam harsolia

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