NEET Practice Questions (MCQs) with Answers & Solutions

When potassium permanganate ($KMnO_4$) is passed through an acidified hydrogen sulfide ($H_2S$) solution, the $KMnO_4$ (a strong oxidizing agent) oxidizes the $H_2S$ to sulfur (S), while itself being reduced. The reaction is:

$2KMnO_4 + 3H_2SO_4 + 5H_2S → 2MnSO_4 + K_2SO_4 + 8H_2O + 5S$.

Therefore, the product formed is sulfur (S).

Arsenic trisulfide (As₂S₃) is soluble in ammonium carbonate ((NH₄)₂CO₃). This is a qualitative analysis technique used to separate group sulfides in analytical chemistry. The solubility of As₂S₃ in (NH₄)₂CO₃ is due to the formation of soluble complex ions.

When acetic acid and potassium ferrocyanide (K₄[Fe(CN)₆]) are added to a copper salt, a chocolate precipitate of copper ferrocyanide (Cu₂[Fe(CN)₆]) is formed. This reaction is used in qualitative inorganic analysis to test for the presence of copper ions.

When HCl is added to a solution of stannous sulphide (SnS) in yellow ammonium sulphide, tin(IV) sulphide ($SnS_2$) is precipitated. The reaction can be written as:

$$ (NH_4)_2SnS_3 + 2HCl ightarrow SnS_2 + 2NH_4Cl + H_2S $$

Mercurous ions ($Hg^+$) form a white precipitate of mercurous chloride (Hg2Cl2) when HCl is added to its aqueous solution:

$$ 2Hg^+ + 2Cl^- ightarrow Hg_2Cl_2 (s) $$

In the qualitative analysis of the IVth group cations, the reagent used is hydrogen sulfide ($H_2S$) in an alkaline medium. This reagent helps to precipitate the cations as their respective sulfides.

When $Al^{3+}$ and $OH^-$ are mixed, they form a precipitate of aluminum hydroxide ($Al(OH)_3$). This is a common reaction in qualitative analysis.