Question

A mixture contains $C{u}^{2+}$, $A{l}^{3+}$, and $N{i}^{2+}$. Following steps have been adopted but written in disorder

I: Filter, boil off $H_{2}S$ gas and add $N{H}_{4}Cl$; heat and add $N{H}_{4}OH$
II: Filter, add $N{H}_{4}OH$ and pass $H_{2}S$ gas.
III: pass $H_{2}S$ gas into an acidified solution of the mixture.

Steps will be used in the following order :

• A. I, II, III
• B. III, I, II
• C. III, II, I
• D. I, III, II

Answer 1

Answer: (B)

III, I, II

As $C{u}^{+2}$ belongs to group IIA so we first pass $H_{2}S$ gas into acidified solution of mixture and black ppt of CuS forms.

Then as $A{l}^{+3}$ belongs to III group so we filter, boil off $H_{2}S$ gas and add $N{H}_{4}Cl$; heat and add $N{H}_{4}OH$,

white ppt of $Al(OH{)}_3$ forms.

After this we filter off ppt and add $N{H}_{4}OH$ and pass $H_{2}S$ gas,

$C{o}^{+2}$ reacts with $H_{2}S$ gas and black ppt of CoS forms.