Question

A sulphide of group IV cation dissolves in in hydrochloric acid to form its chloride. On addition of $NaOH$ solution, it gives white precipitate which is soluble in excess $NaOH$ solution on heating. The cation is of:

• A. $Ca$
• B. $Zn$
• C. None of the above.
• D. $Ni$

Answer 1

The correct option is B $Zn$

Analysis of Group IV Cations
Tests for Zinc ions $\left(Z{n}^{2+}\right)$
Zinc sulphide dissolves in hydrochloric acid to form zinc chloride
Reaction:
$ZnS+2HCl\to ZnC{l}_2+H_{2}S$
On addition of sodium hydroxide solution, it gives white precipitate of zinc hydroxide which is soluble in excess $NaOH$solution on heating confirming the presence of $Z{n}^{2+}$ ions.

Reaction:

$ZnC{l}_2+2NaOH\to \underset{\text{white ppt.}}{Zn(OH{)}_2}\downarrow +2NaCl$

$Zn(OH{)}_2+2NaOH\to \underset{\text{Sodium zincate}\text{(Soluble)}}{N{a}_{2}Zn{O}_2}+2H_{2}O$