Question

When a mixture of $NaCl , K _{2} Cr _{2} O _{7}$ and conc. $H _{2} SO _{4}$ is heated in a dry test tube, a red vapor (X) is evolved. This vapor (X) turns an aqueous solution of $NaOH$ yellow due to the formation of $Y . X$ and $Y$, respectively, are:

• A. $CrCl _{3}$ and $Na _{2} Cr _{2} O _{7}$
• B. $CrCl _{3}$ and $Na _{2} CrO _{4}$
• C. $CrO _{2} Cl _{2}$ and $Na _{2} CrO _{4}$
• D. $Cr _{2}\left( SO _{4}\right)_{3}$ and $Na _{2} Cr _{2} O _{7}$

Answer 1

Answer: (C)

$4 NaCl + K _{2} Cr _{2} O _{7}+6 H _{2} SO _{4} \rightarrow 4 NaHSO _{4}+2 KHSO _{4}$
$+2 CrO _{2} Cl _{2}( X )+6 H _{2} O$
$CrO _{2} Cl _{2}+4 NaOH \longrightarrow Na _{2} CrO _{4}( Y )+2 NaCl +2 H _{2} O$
$X = CrO _{2} Cl _{2}$
$Y = Na _{2} CrO _{4}$