Alum

Alums : Alums are the double salt (ionize in water) having general formula------

                           M2’SO4 M2’’’(SO4 )3.24H2O 

where,     

              M’ = mono-valent metal ions (like Na+,K+, Rb+ etc.)

             M’ =  non-metal ion (like Cs+, (NH4)+ etc.)
            M’’’ = Trivalent metal ions (like Al+3, Fe+3, Cu+3, Cr+3 etc.)

examples:-   K2SO4 .Al2(SO4)3.24H2O              Potash Alum.

                    Na2SO4 .Al2(SO4)3.24H2O            Soda Alum.

                   K2SO4 .Fe2(SO4)3.24H2O               Ferric Alum.

                   Na2SO4 .Cr2(SO4)

3.24H2O             Chrome alum.

            

               If M’’’ = Al, then name according to M’.
              If M’’’ = other than Al, then name according to M’’’.

Properties of Alums :

•  Alums are the white crystalline solid generally used to stop bleeding of small cuts.
• If M’ is replaced by M’’ like Zn+2, Cu+2, Fe+2 etc, then the alums are called as Pseudo alums.
  Exam: -     M’’SO4.M2’’’(SO4 )3.24H2O            Pseudo alums
                   Zn SO4.Al2(SO4 )3.24H2O                Pseudo alums.
•  Na2SO4 .Al2(SO4)3.24H2O + Heat → 
  Na2SO4 .Al2(SO4)3  
  + 24H2O

                                                                                            (burnt alum)

• Aqueous solution of alums are acidic in nature.

                                                                                       https://youtu.be/O3D2belxKBs