Question

Question 35
Iron fillings 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 were seen in both the cases. How will you identify the gases evolved?

Answer 1

As part 'A is heated, a compound FeS is formed by the reaction between iron filings and sulphur. When dilute $HCl$ is added to part A, FeS will react with dil $HCl$ to form $H_{2}S$ gas which has smell of rotten eggs and will turn lead acetate paper black.
$Fe\left(s\right)+S\left(s\right)\to FeS\left(s\right)FeS\left(s\right)+2HCI(dil.)\to FeC{l}_2\left(aq\right)+H_{2}S\left(g\right)\left(C{H}_{3}COO{)}_{2}Pb\right(aq)+H_{2}S(g)\to PbS(s)+2C{H}_{3}COOH\text{Lead acetate}\text{Black ppt}\text{Acetic acid}$
As part 'B' is not heated, so B is a mixture of iron filings and sulphur powder. When dil HCI is added to it, iron filings react with dil. $HCl$ to form $H_2$(g) which burns with a 'pop' sound if burning match stick is brought near it.
$Fe\left(s\right)+2HCI(dil.)\to FeC{l}_2\left(aq\right)+H_2\left(g\right)$