Determina el peso molecular de los siguientes compuestos:

1.- K2Cr2O7
                    K    2 X 39 = 78
                    Cr   2 X 52 = 104
                    O    2 X 16 = 112
         PM = 78 + 104 + 112 = 294g/mol

2.- Na2SO4
                    Na   2 X 23 = 46
                    S     1 X 32 = 32
                    O    4 X 16 = 64
          PM = 46 + 32 + 64 = 42g/mol

3.- (NH4)2CO3
                   N   2 X 14 = 28
                   H   8 X 1   = 8
                   C   1 X 12 = 12
                   O  3 X 16  = 48
          PM = 28 + 8 + 12 + 48 = 96g/mol

4.- Na2HPO4
                  Na    2 X 23 = 46
                   H 1 X 1 = 1
                   P 1X 31 = 31
                   O 4 X 16 = 64
          PM = 46 + 1 + 31 + 64 =142g/mol

5.- K3PO4
                   K 3 X 39 = 117
                   P 1 X 31 = 31
                   O 4 X 16 = 64
           PM = 117 + 31 + 64 = 212 g/mol