Question

Because it was written on my textbook that Zn and Al dissolves in acid and alkali, I tried. When I put Al in NaOH solution it reacted immediately. But when I put Zn in the same concentration of NaOH solution it didn't react. I heated and added NaOH and at last it emitted some bubbles.

This is what I observed when I reacted alkali and Al or Zn.
On the contrary, when I put Zn into 9.5% HCl solution it reacted at once. But when I put Al into the same concentration of HCl solution, it took so long until it starts to emit bubbles.
Could anyone explain why there is such a difference?

Answer 1

The reaction rates of aluminum and zinc with sodium hydroxide (NaOH) and hydrochloric acid (HCl) differ due to their unique properties. Zinc reacts promptly with HCl, producing hydrogen gas, while aluminum reacts slowly due to a protective oxide layer. Aluminum reacts readily with NaOH, whereas zinc needs more extreme conditions to react.

Step-by-step explanation:

The differences in reaction rates of aluminum (Al) and zinc (Zn) with sodium hydroxide (NaOH) and hydrochloric acid (HCl) can be explained by the properties of the metals and the nature of the reactions they undergo.

Zinc reacts quickly with hydrochloric acid as shown in the reaction Zn(s) + 2 HCl(aq) → ZnCl₂(aq) + H₂(g), releasing hydrogen gas due to a single-displacement reaction.

In contrast, when aluminum is added to hydrochloric acid, it forms a protective oxide layer that initially slows down the reaction until it becomes sufficiently damaged to allow the acid to react with the metal underneath thereby producing hydrogen gas.

In alkaline solutions, aluminum reacts swiftly due to its amphoteric nature, forming sodium aluminate and releasing hydrogen.

Zinc requires more extreme conditions, such as excess NaOH and heating, to disturb its passive oxide layer, allowing it to react and form sodium zincate and hydrogen as per the reaction Zn(s) + 2NaOH(aq) + 2 H₂O(l) → Na₂Zn(OH)₄(aq) + H₂(g).