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Why do aluminum salts form acidic solutions in water?

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sodium sulfate — acid–base reaction Sodium sulfate, also called Glauber's salt, is, like other salts, the product of an acid-base reaction.

Aluminum salts form acidic solutions in water because of the hydrolysis of the aluminum cation, which is a process best explained by the Brønsted–Lowry theory.

In aqueous solutions, aluminum ions are strongly hydrated, typically existing as the octahedral ion $[A l (H_{2} O)_{6}]^{3 +}$ . Because the aluminum ion is multiply charged, it exerts a strong influence on its coordinated water molecules, enhancing their tendency to lose protons ( $H^{+}$ ).12

The acidity of the solution arises when a proton is transferred from one of these water molecules in the hydration shell to a molecule of the surrounding solvent water. This reaction can be represented by the following equilibrium:

$[A l (H_{2} O)_{6}]^{3 +} ⇌ [A l (O H) (H_{2} O)_{5}]^{2 +} + H^{+}$

The resulting hydronium ion ( $H_{3} O^{+}$ ) is responsible for the acidic properties of the solution. This behavior is a common characteristic of many metal ions in solution, where coordination to a positive metal center increases the acidity of hydrogen-containing ligands like water.123