Question

Small pieces of steel and some powdered rust are taken in two test tubes separately. What will you observe when concentrated hydrochloric acid is poured into both the test tubes? Justify your observation.

Answer 1

(i) Steel in as alloy. It is a mixture in which iron $\left(\mathrm{Fe}\right)$ is the major component and retains its property in steel. So, pieces of steel will liberate hydrogen and effervescence will be observed.

$\mathrm{Fe}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{FeCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

(ii) Now, rust being a compound of iron does not exhibit the chemical property of iron. Rust will dissolve in $\mathrm{HCl}$ due to the formation of ferric chloride $\left({\mathrm{FeCl}}_3\right)$ and no effervescence will be observed in that test tube.

${\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+6\mathrm{HCl}\left(\mathrm{aq}\right)\to 2{\mathrm{FeCl}}_3\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$