Is Aluminum Hydroxide Soluble in Water?

Struggling with chemical properties? Aluminum hydroxide’s behavior in water can be confusing, but understanding it is key. Let’s clarify this important detail for you.

Aluminum hydroxide (Al(OH)₃) is considered insoluble in water. Its solubility is extremely low, at about 0.0001 grams per 100 mL of water. This property is crucial for many of its industrial and pharmaceutical applications, making it act as a suspension rather than a solution.

We’ve established that it’s insoluble in water, but that is not the complete picture. The way aluminum hydroxide behaves can change a lot in different chemical environments. Knowing these details is vital for using it correctly in any application, from pharmaceuticals to industrial processes. Let’s dive deeper into why this is the case and what it means for you.

Is Aluminium Hydroxide Soluble in Water or Not?

Are you seeing conflicting information about aluminum hydroxide’s solubility? This can be frustrating when you need a clear answer for your application. Here’s the definitive breakdown.

For all practical purposes, aluminum hydroxide is insoluble in neutral water. While a tiny amount technically dissolves, it’s so minimal that it’s insignificant. It forms a suspension, where solid particles are dispersed in the water but do not dissolve into the liquid.

In our factory, I see this every day. When we prepare slurries, we mix aluminum hydroxide powder with water. The result is a milky white liquid. If you let it sit, the white particles will eventually settle at the bottom. This is clear proof that it doesn’t dissolve. The term for this is "practically insoluble." This property is central to its function. While it doesn’t react with or dissolve in neutral water, it is amphoteric¹. This means it will dissolve in both strong acids² and strong bases.

Here is a simple table to show its solubility³:

This dual-reactivity is what makes aluminum hydroxide so useful in so many different industries.

Does Al(OH)₃ Dissociate in Water?

Wondering if aluminum hydroxide breaks apart into ions in water? The term ‘dissociation’ can be confusing for insoluble compounds. Let’s clarify what actually happens.

No, aluminum hydroxide (Al(OH)₃) does not significantly dissociate in water. Because it is an insoluble weak base, only an extremely tiny amount of it will break apart into Al³⁺ and OH⁻ ions. The vast majority of the compound remains as a solid.

Dissociation is the process where a compound splits into ions. Strong acids and bases do this completely in water. Aluminum hydroxide, however, is a weak base and is also insoluble. This means it holds together very tightly in water. But, this changes when you add an acid or a base.

Reaction with Acid

In an acidic environment, like the stomach, it readily reacts. The H⁺ ions from the acid attack the Al(OH)₃, causing it to break apart and neutralize the acid⁴.
Al(OH)₃ + 3H⁺ → Al³⁺ + 3H₂O
This is why it’s a great antacid. As a buyer in the pharmaceutical field, Mr. Park, you’ll know this is critical. It neutralizes stomach acid slowly without causing a pH rebound effect, which would happen if it dissociated too easily.

Reaction with Base

In a strong basic solution, it also reacts to form a soluble complex ion⁵.
Al(OH)₃ + OH⁻ → [Al(OH)₄]⁻
Its stability in water but reactivity in other conditions is its most important feature.

Is Elemental Aluminum (Al) Soluble or Insoluble in Water?

Confusing the properties of aluminum metal with its compounds? It’s a common mix-up, but their behaviors in water are completely different. Let’s distinguish between them clearly.

Elemental aluminum (Al) metal is not soluble in water. However, it does react with water, especially if the water is hot. This reaction is usually prevented by a thin, protective layer of aluminum oxide (Al₂O₃) that forms on the metal’s surface.

It’s important not to confuse aluminum metal (Al) with aluminum hydroxide (Al(OH)₃). They are two different things. Aluminum metal has a special property called passivation. When aluminum is exposed to air, it instantly forms a very thin but very tough layer of aluminum oxide (Al₂O₃) on its surface. This layer is like a protective skin. It stops the aluminum metal underneath from reacting with water or other things in the environment. If you were to scratch this layer off, the aluminum metal would react with water to produce aluminum hydroxide and hydrogen gas.

Here’s how they compare:

So, while aluminum is technically reactive, it appears unreactive in daily life. Aluminum hydroxide is simply an insoluble compound.

How Do You Balance the Equation Al(OH)₃ + H₂CO₃ → Al₂(CO₃)₃ + H₂O?

Stuck balancing a tricky chemical equation? Balancing aluminum reactions can be difficult with multiple polyatomic ions involved. I’ll walk you through the simple steps.

To balance this equation, you need 2 Al(OH)₃ + 3 H₂CO₃ → Al₂(CO₃)₃ + 6 H₂O. You should balance the aluminum and carbonate groups first. Then, finish by balancing the hydrogen and oxygen atoms.

Balancing equations is a matter of following a process. This specific reaction is a neutralization between a base, Al(OH)₃, and an acid, H₂CO₃ (carbonic acid). Let’s go step-by-step.

Step-by-Step Balancing

1. Balance the Metals (Al): The left side has 1 Al atom. The right side has 2 Al atoms in Al₂(CO₃)₃. Place a 2 in front of Al(OH)₃.
   2 Al(OH)₃ + H₂CO₃ → Al₂(CO₃)₃ + H₂O

2. Balance Polyatomic Ions (CO₃): The right side has 3 CO₃ groups. The left side only has 1. Place a 3 in front of H₂CO₃.
   2 Al(OH)₃ + 3 H₂CO₃ → Al₂(CO₃)₃ + H₂O

3. Balance Hydrogen (H): Now, count the H atoms. On the left: 2 * 3 = 6 from 2Al(OH)₃, plus 3 * 2 = 6 from 3H₂CO₃. That’s 12 H atoms. On the right, H₂O has 2 H. To get 12, you need 6 H₂O molecules. Place a 6 in front of H₂O.
   2 Al(OH)₃ + 3 H₂CO₃ → Al₂(CO₃)₃ + 6 H₂O

4. Final Check (O): Always verify with oxygen. Left: (2*3) + (3*3) = 15. Right: (3*3) + 6 = 15. It’s balanced!

Conclusion

In short, aluminum hydroxide is insoluble in water. Its true value lies in its unique reactivity with both acids and bases, a key property for many important applications.