Chromyl choride, `CrO_(2)CI_(2)`, is prep[ared by heating a mixture of

Options

A. `CrO_(3)` and NaCI
B. NaCI, `K_(2)Cr_(2)O_(7)` and `MnO_(2)`
C. NaCI, `K_(2)Cr_(2)O_(7)` and NaOH
D. NaCI, `K_(2)Cr_(2)O_(7)` and concentrated `H_(2)SO_(4)`

Answer

D

Explanation

Chromium (VI) dichloride dioxide, `CrO_(2)CI_(2)`, commonly called chromyl chloride may be formed by dissolving the trioxide in strong acid.
`CrO_(3) + 2HCI` `overset (conc. H_(2)SO_(4)) rarr` `CrO_(2)CI_(2) + H_(2)O`
or in some cases by the action of strong acids on salts such as dichromnates,
`K_(2)Cr_(2)O_(7) + 6HCI` `overset (conc. H_(2)SO_(4)) rarr` `2CrO_(2)CI_(2) + 2KCI + 3H_(2)O`
or by direct addition of the halogens to the dioxide. Chromyl chloride is a deep red covalent liquid. It is formed in qualitative analysis to confirm the presence of chloride ions. When concentrated sulphric acid is added to a mixture of solid `K_(2)Cr_(2)O_(7)` and the suspected chloride (NaCI), chromyI chloride is eveolved as a dark red vapour on heating gently. It condenses to a dark red covalent liqwuid which is immediately hydrolysed by solutions of alkalis to give the chromate:
`CrO_(2)CI_(2)(1) + 4OH^(-) (aq) rarr CrO_(4)^(2-) (aq) + 2CI^(-) (aq) + 2H_2)O(1)`
Since bromides and iodides do not give analogous compounds this is specific test for chloride ions.