What is formula for reaction between aluminum chloride and ammonium hydroxide?

Answer 1

The balance equation between aluminum chloride and ammonium hydroxide is incompletely given by:

AlCl3 + 3NH4OH --> Al(OH)3 + 3NH4Cl

as in the case of excess NH4OH, ammonia does form, as with many metals, NH3 complexes and double salts. In this case, the double salt formed, which is apparently stable to 900 C, is AlCl3.(NH3)6. However, if you are a chemistry student or answering a question on an AP Chem exam, please ignore as I would seriously doubt the state of knowledge on real world chemistry among our educators (if any are aware please comment and I will apologize). The reaction apparently proceeds at room temperature as:

Al(OH)3 + 3 NH4Cl + 3 NH4OH --> AlCl3.(NH3)6 + 3 H2O

Note, interestingly sometimes these excess NH4OH reactions can actually be reversed when the extra NH3 is removed.

For further information read paper below or just the provided extract:

"Reaction study of aluminum chloride with ammonia and mechanisms leading to aluminum nitride" by M. Pouget and J. P. Lecompte at the Laboratoire de Matériaux Céramiques et Traitements de Surface, URA CNRS 320, Faculté des Sciences, 123 Avenue Albert Thomas, 87060, Limoges Cedex, France

(Available online 8 December 1999)

"ABSTRACT

The compound formed between AlCl3 and NH3 at room temperature and low temperature, characterized by different analysis methods, corresponds to the formula AlCl3 · 6NH3. This intermediate was heated to 900 °C under an ammonia stream to obtain aluminum nitride in low yield; as by-product NH4Cl was formed during the thermolysis. In order to explain the decomposition mechanisms, two new pyrolysis were realized, under nitrogen and under reduced pressure. These showed formation of Al(NH2)NH in addition to NH4Cl during the thermal decomposition. Al(NH2)NH can react with HCl, which results from the dissociation of NH4Cl, to form AlClNH volatile combination. This is carried out by the gaseous stream during the thermolysis, thereby accounting for the low synthesis yield."