Q37 / 155 · WBJEE 2016 · Chemistry

Which of the following statement(s) is (are) correct when a mixture of $\mathrm{NaCl}$ and $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ is gently warmed with conc. $\mathrm{H}_{2} \mathrm{SO}_{4} ?$

  • Correct answer
    A
    A deep red vapour is evolved
  • Correct answer
    B
    The vapour when passed through NaOH solution, gives a yellow solution
  • C
    Chiorine gas is also evolved
  • Correct answer
    D
    Chromyl chioride is formed

Solution

(A) When $\mathrm{NaCl}$ and $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ warmed with $\mathrm{H}_{2} \mathrm{SO}_{4}$ (i.e. in acidic medium), they produce deep red vapours of chromyl chloride $\left(\mathrm{CrO}_{2} \mathrm{Cl}_{2}\right)$ (B) When NaOH is passod, the product $CrO_{3}$, formed In step (a) will react with NaOH and gives yellow colour solution (C) Chlorine gas is not evolved, thus false (D) In the given reaction, chromyl chloride $\left(\mathrm{CrO}_2\mathrm{Cl}_{2}\right)$ is formed. All reactions are as follows (i) $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+2 \mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow 2 \mathrm{KHSO}_{4}+2 \mathrm{CrO}_{3}+\mathrm{H}_{2} \mathrm{O}$ (ii) $\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{NaHSO}_{4}+\mathrm{HCl}$ (iii) $\mathrm{CrO}_{3}+2 \mathrm{HCl} \longrightarrow \mathrm{CrO}_{2} \mathrm{Cl}_{2}$ (iv) $\mathrm{CrO}_{2} \mathrm{Cl}_{2}+2 \mathrm{NaOH} \longrightarrow \mathrm{Na}_{2} \mathrm{CrO}_{4}+2 \mathrm{HCl}$

Hence, the correct answer is options: 'A', 'B', 'D'.

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