Question

A solution of a salt in concentrated $H_{2}S{O}_4$ turns a white paste of starch containing potassium iodide blue. The salt may be a:

• A. chloride
• B. carbonate
• C. bromide
• D. acetate

Answer 1

The correct option is C bromide

The salt is a bromide salt. When it reacts with concentrated sulphuric acid, bromine gas is released which turns starch containing potassium iodide blue.
$B{r}^{-}+2H_{2}S{O}_4\to B{r}_2\downarrow +S{O}_2+S{O}_4^{2-}+H_{2}O$
$2I^{-}+B{r}_2\to 2B{r}^{-}+I_2\downarrow$
$I_2+\text{starch}\to \text{blue colour solution}$