Question

Hydrogen sulphide (H₂S) is a strong reducig agent. Which of the following reactions shows its reducing action

(a) Cd(NO₃)₂+ H₂S --------- CdS+ 2HNO_​3
(b) CuSO₄+ H₂S ------------ CuS + H₂SO₄
(c) 2FeCl₃+ H₂S ------------ 2FeCl₂+ 2HCl + S
(d) Pb(NO₃)₂ + H₂S ---------- PbS + 2CH₃COOH

Answer 1

The third reaction shows the reducing action of hydrogen sulphide. That means it reduces the given salt and that itself get oxidised.
$$\begin{gathered} 2FeC{l}_3+H_{2}S\to 2FeC{l}_2+2HCl+S \\ FeC{l}_3 \\ OxidationstateofFe \\ x+3(-1)=0 \\ x=+3 \\ FeC{l}_2 \\ OxidationstateofFe \\ x+2(-1)=0 \\ x=+2 \\ Thusirongetsreducedfrom+3to+2 \\ Atthesametime{H}_{2}SgetsoxidisedtoS \\ {H}_{2}S \\ 2\left(1\right)+x=0 \\ x=-2 \\ Intherightside \\ S=0 \\ ThusSoxidationstatechangesfrom-2to0 \end{gathered}$$