Iron filings and sulphur were mixed together and


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?


1. In part A iron and sulphur will remain as such in the form of a mixture. On adding dilute hydrochlo-ride acid iron will react to evolve hydrogen gas. The gas can be tested by bringing a burning splinter near its mouth. It will burn with a pop sound.

$\mathrm{Fe}(s)+2 \mathrm{HCl}(a q) \longrightarrow \mathrm{FeCl}_{2}(a q)+\mathrm{H}_{2}(g)$

2. In part ' $B$ ' iron and sulphur will combine on heating to form greyish black solid known as iron sulphide.

$\mathrm{Fe}(s)+5(s) \stackrel{\text { heat }}{\longrightarrow} \mathrm{FeS}(s)$

3. When dilute hydrocloric acid is added to the greyish black mass taken in a tube, a gas with foul smell similar to that of the rotton eggs will evolve. This is hydrogen sulphide $(\mathrm{H} 2 \mathrm{~S})$ Cover or Lid

$\mathrm{FeS}(s)+2 \mathrm{HCl}(a q) \longrightarrow \mathrm{FeCl}_{2}(a q)+\mathrm{H}_{2} \mathrm{~S}(g)$


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