Qualitative Analysis - Result Question 29
29. Which of the following statement(s) is(are) correct when a mixture of $NaCl$ and $K _2 Cr _2 O _7$ is gently warmed with conc. $H _2 SO _4$ ?
(1998, 2M)
(a) A deep red vapour is evolved
(b) The vapour when passed into $NaOH$ solution gives a yellow solution of $Na _2 CrO _4$
(c) Chlorine gas is evolved
(d) Chromyl chloride is formed
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Answer:
Correct Answer: 29. $(a, b, c, d)$
Solution:
When mixture of $NaCl$ is heated with $K _2 Cr _2 O _7$ in concentrated $H _2 SO _4$, red vapour of chromyl chloride $\left(CrO _2 Cl _2\right)$ is produced. Vapours of chromyl chloride when passed through $NaOH$, solution turns yellow due to formation of $Na _2 CrO _4$. Some chlorine gas is also evolved owing to the following side reaction :
$6 Cl^{-}+Cr _2 O _7^{2-}+14 H^{+} \longrightarrow 3 Cl _2(g) \uparrow+2 Cr^{3+}+7 H _2 O$
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