Question

A little amount of salt and an equal amount of solid $K_{2}C{r}_2{O}_7$ in a test tube is taken and $conc.H_{2}S{O}_4$ is added to it. On heating the test tube and passing the evolved gas through $NaOH$ solution, a yellow solution is obtained.
On acidifying above solution, and addding small amount of amyl alcohol and $H_2{O}_2$ , ablue colour is obtained on shaking which confirms the presence of:

• A. Bromide ions
• B. Chloride ions
• C. Iodide ions
• D. None of the above

Answer 1

The correct option is B Chloride ions

A little amount of salt and an equal amount of solid $K_{2}C{r}_2{O}_7$ in a test tube is taken and $conc.H_{2}S{O}_4$ is added to it. On heating the test tube and passing the evolved gas through $NaOH$ solution, a yellow solution is obtained.
Acidify it with $dil.H_{2}S{O}_4$ and add small amounts of amyl alcohol and then $1mL$ of $10\%$ hydrogen peroxide solution.On gentle shaking organic layer turns blue.
This confirms the presence of chloride ions.
$Cr{O}_4^{2-}$ion formed in the reaction of chromyl chloride with sodium hydroxide reacts with hydrogen peroxide to form chromium pentoxide. Chromium peroxide dissolves in amyl alcohol to give blue color

Reaction:
$Cr{O}_4^{2-}+2H^{+}+2H_2{O}_2\to Cr{O}_5+3H_{2}O$