Name: Metal Displacement Reactions
Uploaded: 2019-07-19
Duration: 9 min 12 s
Description: This video describes the displacement reactions based on the reactivity series in which a more reactive element displaces a less reactive one from its aqueou...

Question

Aluminium is higher than iron in the reactivity series. To see if this was true, Ayesha took similar sized pieces of aluminium and iron in test tubes. She added the same volume of dilute hydrochloric acid in each. She noticed that:

Initially there was a more vigorous evolution of gas from the test tube having iron.
After a couple of minutes, aluminium starts reacting much faster than iron and the evolution of gas is much more vigorous.

She was confused. Can you explain to her why this happened?

Accepted Answer

Iron reacts with dilute hydrochloric acid to form ferrous chloride and hydrogen gas.

$Fe (s) + 2 HCl (aq) \to {FeCl}_{2} (aq) + H_{2} (g)$

Aluminium when exposed to the air, forms a layer of aluminium oxide. When dilute hydrochloric acid is added to it, first, the oxide gets removed. The aluminium metal then reacts with the acid to form aluminium chloride. Hence, the vigorous reaction and evolution of gas were observed a couple of minutes after iron.

${Al}_{2} O_{3} (s) + 6 HCl (aq) \to 2 {AlCl}_{3} (aq) + 3 H_{2} O (l)$

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