Question

Which of the following isomers will give a white precipitate with${\mathrm{BaCl}}_2$ solution?

• A. $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5{\mathrm{SO}}_4\right]\mathrm{Br}$
• B. $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{SO}}_4$
• C. $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\left({\mathrm{SO}}_4\right)}_2\right]\mathrm{Br}$
• D. $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4\mathrm{Br}\right({\mathrm{SO}}_4\left)\right]$

Answer 1

The correct option is B

$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{SO}}_4$

The explanation for correct option

(B)$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{SO}}_4$

Displacement reaction

• When an atom or a group of atoms is displaced by another atom in a molecule, it is called a displacement reaction.

Reaction involved

$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{SO}}_4+{\mathrm{BaCl}}_2\to \left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{Cl}}_2+{\mathrm{BaSO}}_4$

• Only if the sulphate ion is absent from the coordination sphere than ${{\mathrm{SO}}_4}^{2-}$ ions precipitate with barium chloride.
• It will only be able to dissociate as an anion in aqueous solution after that.

The explanation for incorrect option

$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{SO}}_4$ will give a white precipitate with${\mathrm{BaCl}}_2$ solution. Hence, options (A), (C), and (D) are incorrect.

Hence, option (B) is correct.$\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Br}\right]{\mathrm{SO}}_4$ will give a white precipitate with${\mathrm{BaCl}}_2$ solution.