Question

NaCl reacts with conc. \( H_2SO_4 \) and \( K_2Cr_2O_7 \) to give reddish fumes (B), which react with NaOH to give yellow solution (C). (B) and (C) respectively are:

• A. \(CrO_2Cl_2, Na_2CrO_4\)
• B. \(Na_2CrO_4, CrO_2Cl_2\)
• C. \(CrO_2Cl_2, KHSO_4\)
• D. \(CrO_2Cl_2, Na_2Cr_2O_7\)

Answer 1

The Correct Option is A

To solve this problem, we need to interpret the chemical reactions based on the given information and identify the compounds involved.

1. We start by considering the reaction of NaCl with concentrated \(H_2SO_4\) and \(K_2Cr_2O_7\). The species formed in this reaction are known to produce chromyl chloride, which has the formula \(CrO_2Cl_2\). This compound appears as reddish vapors. Thus, compound (B) from the question is \(CrO_2Cl_2\). 
2. Next, these reddish fumes of \(CrO_2Cl_2\) react with NaOH. The reaction is as follows:

\[ CrO_2Cl_2 + 4NaOH \rightarrow Na_2CrO_4 + 2NaCl + 2H_2O \]

1. Here, \(Na_2CrO_4\) is the yellow solution formed. Hence, compound (C) is \(Na_2CrO_4\).
2. We have now identified the solutions as (B) and (C), which are \(CrO_2Cl_2\) and \(Na_2CrO_4\) respectively.

Now, let's look at the answer choices:

• \(CrO_2Cl_2, Na_2CrO_4\) - This matches our solution.
• \(Na_2CrO_4, CrO_2Cl_2\) - This is incorrect as the sequence of products is reversed.
• \(CrO_2Cl_2, KHSO_4\) - This is incorrect because \(KHSO_4\) is not involved in the reaction with \(NaOH\) to form the yellow solution.
• \(CrO_2Cl_2, Na_2Cr_2O_7\) - This is incorrect as \(Na_2Cr_2O_7\) is not formed in the reaction with NaOH.

Thus, the correct answer is \(CrO_2Cl_2, Na_2CrO_4\).

Answer 2

The reactions involved are:
NaCl + conc. H₂SO₄ + K₂Cr₂O₇ → CrO₂Cl₂ + KHSO₄ + NaHSO₄ + H₂O
(B) is CrO₂Cl₂ (reddish fumes). On reaction with NaOH, it produces a yellow solution (C) which is Na₂CrO₄:
CrO₂Cl₂ + NaOH → Na₂CrO₄ + NaCl + H₂O