The dand fblock elements - Result Question 55
####55. An acidic solution of ’ $X$ ’ does not give precipitate on passing $H_2 S$ through it. ’ $X$ ’ gives white precipitate when $NH_4 OH$ is added to it. The white precipitate dissolves in excess of $NaOH$ solution. Pure ’ $X$ ’ fumes in air and dense white fumes are obtained when a glass rod dipped in $NH_4 OH$ is put in the fumes. Compound ’ $X$ ’ can be [1999]
(a) $ZnCl_2$
(b) $FeCl_3$
(c) $AlCl_3$
(d) $SnCl_2$
Show Answer
Solution:
- (a) $X \xrightarrow{NH_4 OH}$ White ppt
Given reactions (white precipitate with $H_2 S$ in presence of $NH_4 OH$ ) indicate that ’ $X$ ’ should be $ZnCl_2$ which explains all given reactions.
$ZnCl_2^{2}+2 H_2 O \longrightarrow Zn(OH)_2+2 HCl \uparrow$
White fumes
$Zn(OH)_2 \xrightarrow[\text{ Excess }]{2 NaOH} Na_2 ZnO_2+2 H_2 O$
