Question

A sodium salt of an unknown anion when treated with $MgCl_2$ gives white precipitate only on boiling. The anion is

• A. $SO_4^{2-}$
• B. $HCO_3^-$
• C. $CO_3^{2-}$
• D. $NO_3^-$

Answer 1

Answer: (B)

$HCO_3^-$

Answer 2

$Mg(HCO_3)_2$ on boiling decomposes to give white precipitate of $MgCO_3$ as:
$Mg(HCO_3)_2 (aq) \, \, _{\, \, \rightarrow}^{Heat} MgCO_3 \downarrow + H_2O + CO_2 \uparrow$