Aluminium Hydroxide as Amphoteric Substance

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In summary: So it is not a "reaction showing Al(OH)3 acting as a base toward H+ and as an acid toward OH-".In summary, Aluminium hydroxide is an amphoteric substance that can act as both a Bronsted-Lowry base and a Lewis acid. It may undergo reactions such as Al(OH)_{3}+3H^{+}\rightarrow Al^{3+}+3H_{2}O and Al(OH)_{3}+OH^{-}\rightarrow Al(OH)^{-}_{4}, but it also has the potential for many other reactions, such as autoionisation, in which it can accept a proton or an electron pair.
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[SOLVED] Aluminium Hydroxide as Amphoteric Substance

Homework Statement


Aluminium hydroxide is an amphoteric substance. It can act as either a Bronsted-Lowry base or a Lewis acid. Write a reaction showing [tex]Al(OH)_{3}[/tex] acting as a base toward [tex]H^{+}[/tex] and as an acid toward [tex]OH^{-}[/tex].


Homework Equations


I know that amphoteric means the substance can act both as a base and as an acid. I also know that, to be a Bronsted-Lowry base, the substance needs to be a proton acceptor and to be a Lewis acid, an electron-pair acceptor.


The Attempt at a Solution


My biggest problem is that I'm not sure what they really ask. Since it mentions that aluminium hydroxide is an amphoteric substance, does that mean it reacts with itself? If yes, then I'm clueless. If not, then I attempted the following:

[tex]Al(OH)_{3}+H^{+}\rightarrow Al^{3+}+3H_{2}O[/tex]

and

[tex]Al(OH)_{3}+OH^{-}\rightarrow Al(OH)_{4}[/tex]

However, my attempt is very much "gazing in my crystal ball" kind of science since it isn't based on anything I know but rather on a lot of unfounded assumptions and shooting in the dark which is why I need assistance :smile:

Thanks in advance!

phyz
 
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  • #2
Google aluminates.

Your reactions - while not that far from the correct answer - ar far from being balanced :wink:
 
  • #3
Google aluminates.

Your reactions - while not that far from the correct answer - ar far from being balanced

Oh, yeah...of course...see what happens when you concentrate too hard on tex :smile:

This better?

[tex]Al(OH)_{3}+3H^{+}\rightarrow Al^{3+}+3H_{2}O[/tex]

and

[tex]Al(OH)_{3}+OH^{-}\rightarrow Al(OH)^{-}_{4}[/tex]

and Google you reckon? Mmmmmm...:rolleyes:

Google here I come! :biggrin:
 
  • #4
Solved! :cool:

Thanks Borek! Three thumbs up :wink:
 
  • #5
Just a thought, but could the question be asking for something like this?

[tex]
Al(OH)_{3} + Al(OH)_{3}{+}\rightleftharpoons AlH(OH)_2^+ + AlO(OH)_2^-
[/tex]

This is, as the question states, "a" reaction, where Al(OH)3 bevaes in both ways, one accepting a proton, the other an electron pair. Autoionisation?

Its late, I'm tired, and this has kept me busy for too long, so pleeease tell me if I am completely wrong :P
 
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  • #6
These are equilibrium systems, to some extent such reaction will proceed - along many others. So you are not completely wrong.

What I don't like about the reaction is that it may suggest a little bit too much. It may occur, but for sure it will not dominate the solution.
 

1. What is aluminium hydroxide?

Aluminium hydroxide is a chemical compound with the formula Al(OH)3. It is a white, insoluble powder that is commonly used in industrial and medical applications.

2. How does aluminium hydroxide act as an amphoteric substance?

Amphoteric substances are able to act as both an acid and a base. Aluminium hydroxide can neutralize both acids and bases, making it amphoteric.

3. What are the common uses of aluminium hydroxide?

Aluminium hydroxide is commonly used as an antacid to treat heartburn and stomach ulcers. It is also used in the production of various industrial materials, including paper, ceramics, and plastics.

4. Is aluminium hydroxide safe for consumption?

Yes, aluminium hydroxide is generally considered safe for consumption in small doses. However, large doses over a long period of time may lead to aluminum toxicity, which can cause neurological problems.

5. How is aluminium hydroxide produced?

Aluminium hydroxide is typically produced through the reaction of aluminium sulfate or aluminium chloride with sodium hydroxide. It can also be produced through the Bayer process, which involves the reaction of bauxite ore with sodium hydroxide.

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