Are Aluminium Ions Actually Acidic?

In summary, the CSIRO scientists found that the oxidation of iron pyrites in these area, much of which had been exposed as a result of draining swamps for grazing cattle and the use of floodgates to drain cane fields, released sulfuric acid, which in turn mobilized the aluminium ions in the clays. These ions are also acidic.
  • #1
pivoxa15
2,255
1
In a paragraph in the textbook "When CSIRO scientists were called into investigate, they discovered that the cause was the oxidation of iron pyrites in these area, much of which had been exposed as a result of draining swamps for grazing cattle and the use of floodgates to drain cane fields. This released sulfuric acid, which in turn mobilised the aluminium ions in the clays. These ions are also acidic."

How can aluminium ions be acidic? Is it saying Al(3+) is an acid?
 
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  • #2
I'm not sure exactly what the passage means, but it's probably just saying that the aluminates (or oxides or hydroxides) in the clay are acidic. Many aluminium compounds are known to be amphoteric (notably the oxide and hydroxide) - they will neutralize acids as well as bases, by complexing with the free H+ or OH- in solution. Others are slightly acidic and some are slightly basic.

And when it says "aluminium ions", I'm not sure it necessarily means Al(3+) but it might. Furthermore, in acidic media the ions in solution are probably more like [Al(H2O)n]3+. In any case, that passage is written too casually (lacking any kind of precision of description) to be taken seriously.
 
  • #3
i think it implies [tex][Al(H_{2}O)_{6-n}(OH)_{n}]^{3-n}[/tex]

the way i understood it, the high charge density of the "Al3+" ion dragged in electron density off the water ligands, so the water ligands could be deprotonated to form the above complex (though the number of deprotonations depends on the sulphuric acid concentration) and hydronium ions.
 
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  • #4
So it is talking about Aluminium when part of a compound and that compound being an acid? I know that Al(3+) cannot donate a proton (hence not an acid) unless its a nuclear reaction which I don't think was on the author's mind.
 
  • #5
pivoxa15 said:
So it is talking about Aluminium when part of a compound and that compound being an acid? I know that Al(3+) cannot donate a proton (hence not an acid) unless its a nuclear reaction which I don't think was on the author's mind.
Look for Lewis definition of acidity (more general).
 

1. What makes aluminium ions acidic?

Aluminium ions have a positive charge and a small size, making them highly polarizing. This means that they have a strong attraction to nearby water molecules and can easily strip off their hydrogen ions, resulting in an acidic solution.

2. How do aluminium ions affect the pH of a solution?

When aluminium ions react with water, they form a weak acid known as aluminum hydroxide. This acid increases the concentration of hydrogen ions in the solution, lowering the pH and making it more acidic.

3. Are all aluminium compounds acidic?

No, not all aluminium compounds are acidic. Some compounds, like aluminium oxide, are amphoteric, meaning they can act as both an acid and a base depending on the conditions they are in.

4. Can aluminium ions be found in nature?

Yes, aluminium ions are naturally found in the Earth's crust and are the most abundant metal in the Earth's crust. They can also be found in various minerals and rocks.

5. What are some common uses of acidic aluminium compounds?

Acidic aluminium compounds, such as aluminium sulfate and aluminium chloride, are commonly used in water treatment, as they help to purify and clarify water by removing impurities and solids. They are also used in industries like paper production, textiles, and petroleum refining.

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