Question

Addition of $SnC{{l}_{2}}$ to $HgCl_2$ gives precipitate:

• A. white turning to red
• B. white turning to grey
• C. black turning to white
• D. none of the above

Answer 1

Answer: (B)

white turning to grey

Answer 2

Stannous chloride $\left( SnCl _{2}\right)$ is a good reducing agent. It reduces $HgCl _{2}$ into $Hg$ (grey precipitate), in two steps.
$SnCl _{2}+2 HgCl _{2} \longrightarrow SnCl _{4}+ \underset{\text{white}}{HgCl _{2}} \downarrow$
$SnCl _{2}+ Hg _{2} Cl _{2} \longrightarrow SnCl _{4}+ \underset{\text{grey}}{2 Hg} \downarrow$