Chemistry · Practical Inorganic chemistry (Qualitative Analysis)

JEE Advanced 2019 — Paper 1 — Question 18

The green colour produced in the borax bead test of a chromium(III) salt is due to

Option A:
CrB
Option B:
$\mathrm{Cr}_{2} \mathrm{O}_{3}$
Option C:
$\mathrm{Cr}_{2}\left(\mathrm{~B}_{4} \mathrm{O}_{7}\right)_{3}$
Option D:
$\mathrm{Cr}\left(\mathrm{BO}_{2}\right)_{3}$
Correct

Answer: D

Step-by-step solution

$\mathrm{Cr}\left(\mathrm{BO}_{2}\right)_{3}$

$\mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7} \cdot 10 \mathrm{H}_{2} \mathrm{O} \xrightarrow{\Delta} \mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7} \xrightarrow{\Delta} \mathrm{NaBO}_{2}+\mathrm{B}_{2} \mathrm{O}_{3}$

$\mathrm{Cr}_{2} \mathrm{O}_{3}+\mathrm{B}_{2} \mathrm{O}_{3} \longrightarrow \underset{\text { (green colour bead) }}{\mathrm{Cr}\left(\mathrm{BO}_{2}\right)_{3}}$

Answer key and solution verified before publishing.

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Exam: JEE Advanced 2019
Paper: Paper 1
Subject: Chemistry
Chapter: Practical Inorganic chemistry (Qualitative Analysis)
Topic: Introduction to Qualitative Analysis + Preliminary Tests - Dry Tests