NaCl reacts with conc. H_2 SO_4 and K_2 Cr_2 O_7 to give reddish fumes (B), which react with NaOH to give yellow solution (C). (B) and (C) respectively are ;

D and F Block Elements PYQ — JEE Main 2024 · 27 Jan · Shift 1 · Q18 with Solution

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Correct answer: A

Identify the reaction

When a chloride salt such as $\mathrm{NaCl}$ is heated with conc. $\mathrm{H_2SO_4}$ and $\mathrm{K_2Cr_2O_7}$ , the well-known chromyl chloride test occurs.

The reddish fumes produced are chromyl chloride, $\mathrm{CrO_2Cl_2}$ .

So,

(B)=\mathrm{CrO_2Cl_2}

Why is chromyl chloride formed?

Conc. $\mathrm{H_2SO_4}$ first generates $\mathrm{HCl}$ from $\mathrm{NaCl}$ , and in the presence of dichromate under strongly acidic conditions, chromyl chloride is formed as red vapours.

A representative overall reaction is:

4\mathrm{NaCl}+\mathrm{K_2Cr_2O_7}+6\mathrm{H_2SO_4} \rightarrow 2\mathrm{CrO_2Cl_2}+2\mathrm{KHSO_4}+4\mathrm{NaHSO_4}+3\mathrm{H_2O}

Reaction of $\mathrm{CrO_2Cl_2}$ with $\mathrm{NaOH}$

Chromyl chloride reacts with alkali to give a yellow solution of sodium chromate:

\mathrm{CrO_2Cl_2}+4\mathrm{NaOH}\rightarrow \mathrm{Na_2CrO_4}+2\mathrm{NaCl}+2\mathrm{H_2O}

The yellow colour is due to the chromate ion, $\mathrm{CrO_4^{2-}}$ .

Hence,

(C)=\mathrm{Na_2CrO_4}

Match with options

A: $\mathrm{CrO_2Cl_2},\ \mathrm{Na_2CrO_4}$ ✔️
B: reversed order ✘
C: second compound wrong ✘
D: $\mathrm{Na_2Cr_2O_7}$ is orange, not the yellow chromate solution ✘

Therefore, the correct option is:

\boxed{A}

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View written solutionFree

Correct answer: A

Identify the reaction

When a chloride salt such as $\mathrm{NaCl}$ is heated with conc. $\mathrm{H_2SO_4}$ and $\mathrm{K_2Cr_2O_7}$ , the well-known chromyl chloride test occurs.

The reddish fumes produced are chromyl chloride, $\mathrm{CrO_2Cl_2}$ .

So,

(B)=\mathrm{CrO_2Cl_2}

Why is chromyl chloride formed?

Conc. $\mathrm{H_2SO_4}$ first generates $\mathrm{HCl}$ from $\mathrm{NaCl}$ , and in the presence of dichromate under strongly acidic conditions, chromyl chloride is formed as red vapours.

A representative overall reaction is:

4\mathrm{NaCl}+\mathrm{K_2Cr_2O_7}+6\mathrm{H_2SO_4} \rightarrow 2\mathrm{CrO_2Cl_2}+2\mathrm{KHSO_4}+4\mathrm{NaHSO_4}+3\mathrm{H_2O}

Reaction of $\mathrm{CrO_2Cl_2}$ with $\mathrm{NaOH}$

Chromyl chloride reacts with alkali to give a yellow solution of sodium chromate:

\mathrm{CrO_2Cl_2}+4\mathrm{NaOH}\rightarrow \mathrm{Na_2CrO_4}+2\mathrm{NaCl}+2\mathrm{H_2O}

The yellow colour is due to the chromate ion, $\mathrm{CrO_4^{2-}}$ .

Hence,

(C)=\mathrm{Na_2CrO_4}

Match with options

A: $\mathrm{CrO_2Cl_2},\ \mathrm{Na_2CrO_4}$ ✔️
B: reversed order ✘
C: second compound wrong ✘
D: $\mathrm{Na_2Cr_2O_7}$ is orange, not the yellow chromate solution ✘

Therefore, the correct option is:

\boxed{A}

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