Question

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?

Answer 1

Formation of Iron sulfide

1. A chemical reaction occurs when iron filings and sulfide powder are mixed and heated combination reaction takes place and ferrous sulfide $\left(\mathrm{FeS}\right)$is formed.
2. The equation for the reaction that produces the iron sulfide is:

$\underset{\mathrm{Iron}}{\mathrm{Fe}}+\underset{\mathrm{sulphur}}{\mathrm{S}}\to \underset{\mathrm{Iron}\mathrm{sulphide}}{\mathrm{FeS}}$

• Part A:

Reaction of Iron sulfide with Hydrochloric acid and heated

1. When HCl is added to this mixture ferric chloride is formed and Hydrogen sulfide gas is produced.
2. Reaction:

$\underset{\mathrm{Iron}\mathrm{sulphide}}{\mathrm{FeS}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\stackrel{∆}{\to }\underset{\mathrm{Ferric}\mathrm{chloride}}{{\mathrm{Fe}}_2{\mathrm{Cl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{sulphide}}{{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)}$

Test : The foul rotten egg smell of Hydrogen Sulfide is the indicator of ${\mathrm{H}}_2\mathrm{S}$ production.

• Part B:

Reaction of Iron sulfide with Hydrochloric acid without heat

1. When dilute$\mathrm{HCl}$ is added to setup B Hydrogen gas is evolved and sulfide does not take part in the reaction.
2. Reaction:

$\underset{\mathrm{Iron}}{2\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{6\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Ferric}\mathrm{Chloride}}{2{\mathrm{FeCl}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{3{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Test: When a burning match stick is brought near the evolved gas, the matchstick burns with a pop. This is the indication of the production of Hydrogen gas.

Iron filings and sulfide were mixed together they form Iron sulfide , and in part A , hydrogen sulfide gas is evolve and in part B hydrogen gas is evolved.