Acidity of Aluminium Hydroxide

Aluminium hydroxide, with Al(OH)3Al(OH)3​, is amphoteric, meaning it can act as both an acid and a base. Its acidity or basicity depends on the environment it is in:

1. In Acidic Solutions: can react with acids, acting as a base. For example, it reacts with hydrochloric acid:Al(OH)3+3HCl→AlCl3+3H2OAl(OH)3​+3HCl→AlCl3​+3H2​O
2. In Basic Solutions: can also react with bases, acting as an acid. For example, it reacts with sodium hydroxide –Al(OH)3+NaOH→Na[Al(OH)4]Al(OH)3​+NaOH→Na[Al(OH)4​]Here, Na[Al(OH)4]Na[Al(OH)4​] is sodium tetrahydroxoaluminate, indicating that has accepted an additional hydroxide ion.

Chemical Properties:

• Weakly Basic Nature: In general,  is weakly basic. This is due to the partial solubility in water, where it slightly increases the pH of the solution.
• Solubility in Water: Aluminium hydroxide is not very soluble in water, and its solubility decreases as the pH increases. This low solubility limits its ability to affect the pH significantly unless in the presence of strong acids or bases.

pH Considerations:

• The pH of a saturated solution of aluminium hydroxide is slightly basic, typically around 8-9. However, this can vary based on the specific conditions and the presence of other compounds in the solution.

Overall, the amphoteric nature of aluminium hydroxide makes it versatile in reacting with both acids and bases, but its weakly basic property is more prominent in neutral or slightly basic aqueous environments.