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  4. Aqueous solution of a salt (A) forms a dense white precipitate with BaCl2 solution. The precipitate dissolves in dilute HCl to produce a gas (B) which decolourises acidified KMnO4 solution A and B respectively are :

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Q. Aqueous solution of a salt $(A)$ forms a dense white precipitate with $BaCl_2$ solution. The precipitate dissolves in dilute $HCl$ to produce a gas $(B)$ which decolourises acidified $KMnO_4$ solution
$A$ and $B$ respectively are :

KCETKCET 2020The d-and f-Block Elements

Solution:

The corresponding reactions are

$BaCl _{2}+ Na _{2} SO _{3} \rightarrow BaSO _{3}+2 NaCl$

$BaSO _{3}+2 HCl \rightarrow BaCl _{2}+ SO _{2}+ H _{2} O$

Salt $A$ is $Na _{2} SO _{3}$ and the dense white precipitate is $BaSO _{3}$ (Barium sulfite).

Gas $B$ is $SO _{2}$. It decolourises acidified $KMnO _{4}$ solution because of its reducing nature.

The corresponding reaction is:

$2 KMnO _{4}+5 SO _{2}+2 H _{2} O \rightarrow K _{2} SO _{4}+2 MnSO _{4}+2 H _{2} SO _{4}$