Sodium hydroxide is added to a cylinder of aluminum nitrate, precipitating out aluminum hydroxide.  When additional base is added, the precipitate dissolves.  The reactions can then be reversed with the addition of hydrochloric acid.  The precipitate will reappear and then redissolve.


 Al(NO3)3(aq) + 3NaOH(aq) → Al(OH)3(s) + NaNO3(aq)

 Al(OH)3(s) + OH-(aq)  Al(OH)4-(aq)

 Al(OH)4-(aq) + H+(aq)  Al(OH)3(s)

 Al(OH)3(s) + 3H+(aq)  Al3+ (aq) + 3H2O(l)

 To Conduct Demonstration:

  1.        Turn on stir plate and add NaOH solution until Al(OH)3 precipitates.
  2.        Add more NaOH until the hydroxide precipitate dissolves.
  3.        Add HCl until the precipitate is visible.
  4.        Continue to add HCl until the hydroxide is re-dissolved.


Goggles should be worn. 


Shakhashiri, B.Z. Chemical Demonstrations:  A Handbook for Teachers of Chemistry1983.