Question

Which of the reaction is true with respect to $H_{2}S$?

• A. It turns ferric ions to ferrous ions.
• B. It turns $S{O}_2$ to $S$
• C. It gives positive methylene blue test
• D. none of the above

Answer 1

Answer: (A), (B), (C)

It gives positive methylene blue test
It turns ferric ions to ferrous ions.
It turns $S{O}_2$ to $S$

$A.)$ $H_{2}S+2F{e}^{+3}⟶S{S}^0+2F{e}^{2+}+2H^{+}$

$H_{2}S$ in this reaction is oxidized to elemental sulfur. At the same time, $F{e}^{+3}$ is reduced to $F{e}^{2+}$.

$B.)$ $2H_{2}S+S{O}_2⟶3S+2H_{2}O$

Therefore, when $hydrogen$ $sulfide$ gas is passed through $sulfur$ $dioxide$, then elemental $sulfur$ is produced.

$C.)$ $H_{2}S$ gives positive methylene blue test. In this test, $hydrogen$ $sulfide$ concerts $N,$ $N$ $demethyle$-$p$-$phenylenediamine$ directly to methylene blue in the pressure of metal oxidizing agents.

$\text{Amount of sulfide present}\propto \text{Intensity of methylene blue color.}$