1
$\begingroup$

Aluminium hydroxide is not soluble in water at all, however I was doing some reading and read that it does in fact dissolve in a solution of sodium hydroxide. This just seemed a bit strange to me, so I was wondering if anyone could explain why this is the case.

|improve this question
$\endgroup$
1
$\begingroup$

That's because $\ce{Al(OH)3}$ is amphoteric in nature, it acts as both acid and base. When you drop a chunk of $\ce{Al(OH)3}$ into a solution of $\ce{NaOH}$, you would get a soluble salt, which is sodium aluminate, and some extra water.

$$\ce{Al(OH)3 + NaOH -> Na[Al(OH)4]}$$

|improve this answer
$\endgroup$
  • 1
    $\begingroup$ Out of curiosity, is there any way to tell if a substance is amphoteric? $\endgroup$ – Etched Jul 11 '17 at 3:41
  • $\begingroup$ @Etched Yes, but you need to analyze the structure carefully. In the case of $\ce{Al(OH)3}$, it acts as a base since the $\ce{Al-O}$ bonds are broken, releasing $\ce{OH-}$. But at the same time, it can also accept $\ce{OH-}$ due to the presence of empty electron orbitals that can grasp onto electrons. This is just a little description, if you need more info, please ask a new question. $\endgroup$ – Pritt Balagopal Jul 11 '17 at 3:46
  • 3
    $\begingroup$ Another major point is that saying"Aluminium hydroxide is not soluble" isn't entirely correct. When a chemist says "not soluble" what he is really saying is that the solubility is very low. // I'd write the reaction as $$\ce{Al(OH)3 + NaOH -> Na^+[Al(OH)4]^- }$$ $\endgroup$ – MaxW Jul 11 '17 at 3:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.