•      Mg(OH)2  → Mg+2   +  2OH-

              NH4+  is strong conjugate acid which attract OH- ions and convert to NH4OH

            2NH4+  +2 OH-  →2 NH4OH

            More Mg(OH)2 will ionize to provide OH- ions to NH4+

•      2: hydroxides of Aluminium  Al (OH)3 

•      Aluminium hydroxide, like aluminium oxide, is amphoteric - it has both basic and acidic properties. It is prepared by

•      1: by the reaction of ammonium salt with alkali:

•      Al2  (SO4 )3  +  6NH4OH   →3(NH4)2 SO4  +2 Al(OH)3

•      2: By the hydrolysis of AlCl3 .

•      AlCl3  + 3H2O → Al(OH)3  + 3HCl

•      Other Hydroxides:

•      The elements Si , P ,S and Cl of period 3 form hydroxides in which OH group is covalently bonded to these elements like Si(OH)4 , H3PO4 ,H2SO4 , HClO4 

•      None of these contains hydroxide ions. In each case the -OH group is covalently bound to the Period 3 element, and in each case it is possible for the hydrogens on these -OH groups to be removed by a base. In other words, all of these compounds are acidic.