Qualitative Analysis - Result Question 26
####26. The pair(s) of ions where both the ions are precipitated upon passing $H _2 S$ gas in presence of dilute $HCl$, is (are)
(a) $Ba^{2+}, Zn^{2+}$
(b) $Bi^{3+}, Fe^{3+}$
(c) $Cu^{2+}, Pb^{2+}$
(d) $Hg^{2+}, Bi^{3+}$
(2015 Adv.)
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Answer:
Correct Answer: 26. (c,d)
Solution:
- Only radicals of I and II group of qualitative analysis get precipitated with $H _2 S$ in the presence of dilute $HCl$.
(c) $Cu^{2+}+H _2 S \xrightarrow{H^{+}} CuS \downarrow$
$$ Pb^{2+}+H _2 S \xrightarrow{H^{+}} PbS \downarrow $$
(d) $Hg^{2+}+H _2 S \xrightarrow{H^{+}} HgS \downarrow$ Black
$$ Bi^{3+}+H _2 S \xrightarrow{H^{+}} \underset{\text { Brown ppt }}{Bi _2 S _3 \downarrow} $$
$Ba^{2+}, Zn^{2+}$ and $Fe^{3+}$ are not precipitated as sulphide.
