Iron filings and sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’ was heated strongly while Part ‘B’ was not heated. Dilute hydrochloric acid was added to both the Parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?

Part A was heated strongly.

The equation given below shows the reaction:

Fe (s) + S (s) FeS (s)

When dilute hydrochloric acid was added to Part A, following reaction took place:

FeS + 2 HCl (aq) → FeCl₂+ H₂S

H₂S gas is evolved.

H₂S gas formed has a foul smell (as that of rotten eggs) and on passing through lead acetate solution, it turns the solution black.

(CHCOO)₂Pb(ag) + H₂S(g) → PbS(s) + 2CH₃COOH
Lead acetate Black ppt Acetic acid

Part B is not heated.

Fe (s) + S (s) (mixture of iron filings and sulphur): Not heated

When dilute HCl is added to Part B, following reaction took place:

Fe (s) + S (s) + 2 HCl (aq) → FeCl₂ + H₂

Hydrogen gas is evolved and sulphur remains unreacted.

Hydrogen gas burns with a pop sound if burning match stick is brought near it.
Fe (s)+ 2HCI (dil.) → FeCI₂(ag) + H₂(g)