ABC26IN0016 · Acids and Bases

Subject: Inorganic Chemistry · Chapter: Acids and Bases · Topic: Acid and Bases – General · Exam: CSIR-NET DEC 2019 · Marks: 2 · Difficulty: Easy

Choose the equilibria from the following that are NOT favoured to go to right
\[ \begin{array}{l} \text{(A) } \mathrm{As_2S_5} + 5\mathrm{HgO} \xleftrightarrow{\text{gives}} \mathrm{As_2O_5} + 5\,\mathrm{HgS} \\ \text{(B) } \mathrm{La_2(CO_3)_3} + \mathrm{Bi_2S_3} \xleftrightarrow{\text{gives}} \mathrm{La_2S_3} + \mathrm{Bi_2(CO_3)_3} \\ \text{(C) } \mathrm{CaSO_4} + \mathrm{CaS} \xleftrightarrow{\text{gives}} \mathrm{CdS} + \mathrm{CaSO_4} \\ \text{(D) } \mathrm{BeF_2} + \mathrm{HgI_2} \xleftrightarrow{\text{gives}} \mathrm{BeI_2} + \mathrm{HgF_2} \end{array} \]
(a)A and B
(b)A and C
(c)B and C
(d)B and D
Answer
Answer (as printed): D
Explanation
This can be explained with the help of HSAB principle. $\mathrm{Be^{2+}}$ is hard acid hence favour hard base $\mathrm{F^{-}}$ Also $\mathrm{La^{3+}}$ is hard acid, thus favour hard base $\mathrm{CO_3^{2-}}$ Therefore, process B and D are not feasible.
\[ \mathrm{La_2(CO_3)_3 + Bi_2S_3 \xleftrightarrow{\text{gives}} La_2S_3 + Bi_2(CO_3)_3} \]
$\mathrm{HA} \quad \mathrm{HB} \leftarrow \mathrm{HA} \quad \mathrm{SB}$
\[ \mathrm{BeF_2 + HgI_2 \xleftrightarrow{\text{gives}} BeI_2 + HgF_2} \]
HA HB \leftarrow HA SB

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