Reaction of BeO with ammonia and hydrogen fluoride gives A… — JEE Main 2023 Chemistry PYQ

JEE Main 2023 · 24 Jan · Shift 1 · Paper-1(B.E./B. Tech.)

Reaction of BeO with ammonia and hydrogen fluoride gives A which on thermal decomposition gives

\text{BeF}_2

and

\text{NH}_4\text{F}

. What is 'A' ?

A.
$(\text{NH}_4)\text{BeF}_3$
B.
$(\text{NH}_4)\text{Be}_2\text{F}_5$
C.
$\text{H}_3\text{NBeF}_3$
D.
$(\text{NH}_4)_2\text{BeF}_4$

Show answer and solution

Correct option: D

Solution

BeO reacts with excess HF and NH₃ to form (NH₄)₂BeF₄. On thermal decomposition:

(NH₄)₂BeF₄ → BeF₂ + 2NH₄F

This balanced decomposition exactly matches the products stated, with 2 moles of NH₄F produced per mole of BeF₂. Be²⁺ in this compound is tetrahedrally coordinated by four F⁻ ions forming the [BeF₄]²⁻ anion, balanced by two NH₄⁺ cations, which is consistent with Be's tendency to achieve a stable 4-coordinate environment.

[JEE Main 2023 · 24 Jan · Shift 1 · Paper-1(B.E./B. Tech.)]

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