BioMedical Admissions Test (BMAT) Practice Test

When excess sodium hydroxide (NaOH) is added to aluminum hydroxide (Al(OH)3), the precipitate dissolves to form a colorless solution. This occurs because Al(OH)3 is amphoteric, meaning it can react with both acids and bases. In the presence of excess NaOH, Al(OH)3 reacts to form the soluble aluminate ion, [Al(OH)4]⁻. This reaction results in the dissolution of the white precipitate and leads to the formation of a clear solution, which is characteristic of the behavior of amphoteric hydroxides when treated with strong bases. Thus, the addition of excess NaOH effectively transforms the previously solid precipitate into a dissolved form in the solution.