Which of the following statement is/are correct when a mixture of NaCl and K2 Cr- O, is gently w

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Which of the following statement is/are correct when a...

Which of the following statement is/are correct when a mixture of $\mathrm{NaCl}$ and $\mathrm{K}_{2} \mathrm{Cr}_{-} \mathrm{O}$, is gently warmed with conc. $\mathrm{H}_{2} \mathrm{SO}_{4}$ ? (a) The vapour when passed into $\mathrm{NaOH}$ solution gives a yellow solution of $\mathrm{Na}_{2} \mathrm{CrO}_{4}$. (b) A decp red vapour is cvolved. (c) Chlorinc gas is cvolved. (d) Chromyl chloride is formed.

Which of the following statement is/are correct when a mixture of $\mathrm{NaCl}$ and $\mathrm{K}_{2} \mathrm{Cr}_{-} \mathrm{O}$, is gently warmed with conc. $\mathrm{H}_{2} \mathrm{SO}_{4}$ ?
(a) The vapour when passed into $\mathrm{NaOH}$ solution gives a yellow solution of $\mathrm{Na}_{2} \mathrm{CrO}_{4}$.
(b) A decp red vapour is cvolved.
(c) Chlorinc gas is cvolved.
(d) Chromyl chloride is formed.

Key Concepts

Chromyl Chloride Test

This is a qualitative test for the presence of chloride ions in a sample. When a chloride-containing compound is heated with concentrated sulfuric acid and a chromate source, a red volatile compound, chromyl chloride, is generated. The presence of red vapours and its reaction (such as hydrolysis to give a yellow solution of chromate ions when treated with a base) confirms the existence of chloride ions.

Acid–Base Equilibrium of Chromate and Dichromate

Chromate (CrO4²?) and dichromate (Cr2O7²?) ions exist in an equilibrium that is dependent on the pH of the solution. Under acidic conditions, chromate ions are converted into dichromate ions. This acid-induced transformation is critical in reactions used for tests like the chromyl chloride test, where the effective species involved may be generated in situ.

Properties and Hydrolysis of Chromyl Chloride

Chromyl chloride (CrO2Cl2) is a deep red, volatile compound that can be produced in situ and serves as an indicator in qualitative analyses. When the vapour is passed into a base such as NaOH, it hydrolyzes to form chromate ions, which impart a characteristic yellow color to the solution. This hydrolysis confirms its formation and is a key step in the test procedure.

Avoidance of Chlorine Gas Formation

In the context of the chromyl chloride test, although chloride ions and sulfuric acid can sometimes produce chlorine gas under different conditions, the specific reaction conditions (including the presence of a chromate source) favor the formation of chromyl chloride rather than chlorine gas. Understanding the reaction pathway is essential to correctly interpret the observations.

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