Why does the reaction between acid and aluminium start slow and then speed up?

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Discussion Overview

The discussion centers on the observation that the reaction between acid and aluminum starts slowly and then accelerates. Participants explore potential explanations for this behavior, focusing on the chemical interactions involved, particularly the role of aluminum oxide.

Discussion Character

  • Homework-related
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant suggests that the high melting and boiling points of aluminum might explain the reaction behavior, but later retracts this idea.
  • Another participant points out that aluminum reacts with oxygen to form aluminum oxide, which may coat the aluminum and affect its reactivity with acid.
  • A subsequent reply clarifies that the acid first reacts with the aluminum oxide before reacting with the underlying aluminum.
  • Some participants express uncertainty about the specifics of the reaction progression and the role of aluminum oxide in the reaction.
  • There is a suggestion that the slow initial reaction is due to the presence of aluminum oxide, while the faster reaction occurs once the oxide layer is penetrated.

Areas of Agreement / Disagreement

Participants generally agree that aluminum oxide plays a significant role in the reaction dynamics, but there is no consensus on the exact mechanisms or details of the reaction process.

Contextual Notes

Some claims about the reactivity of aluminum and aluminum oxide remain unresolved, and participants express varying levels of understanding regarding the chemical interactions involved.

rahmatkat
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Can anyone help me with this homework question? it was like this:

The reaction between the acid and aluminium is slow in the beginning and then gets faster. Give an explanation for this observation.

Thanks.
 
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Do you have ideas of your own?
 
Last edited by a moderator:
Well, my idea is that it has a high melting and boiling point and its resist corrosion, unfortunately my answer above is wrong and i don't have any other idea why it reacts slowly with acid at first and then faster.
 
It has nothing to do with melting points. What do you know about aluminum reacting with oxygen?
 
Last edited by a moderator:
Oh, I get it now, aluminium react with oxygen gas in the air and produce Aluminium Oxide forming in the outside part of an aluminium metal right? So when that aluminium metal is reacted with an acid, Aluminium Oxide reacts first with the acid and when it finished reacting with it, the acid then react with the aluminium which being coated by Aluminium Oxide.
 
You started your answer (post #5) well and then you smashed your logic as you progressed.
 
Oh,
So Aluminium Oxide did form?
As for the reaction, the oxygen present in the Alumium Oxide react first with the acid and when that Oxygen dissapear, the acid then react with Aluminium, is that rihgt?
 
You must be on the correct track. Aluminum is a reactive metal, but Aluminum oxide is much less reactive. I am not myself fully in tune with the way the reaction with acid should progress; but the acid solution first meets the oxide, and then meets the mostly unreacted aluminum (which is then in contact to react).
 
You are homing on the target. Slow part - reaction with oxide, fast part - reaction with bare metal.
 
Last edited by a moderator:
  • #10
Thanks guys, I think I get it now.
 

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