Find the ratio by mass of the combining elements in the following compounds
(a) al2(so4)3
(b) cacl2

The given compound is Aluminum sulfate, Al2(SO4)3:

Molar masses:

Aluminum = 27 g/mol
Sulfur = 32 g/mol
Oxygen = 16 g/mol

The total molar mass is 342 g/mol
The ratio by mass of the elements:

Aluminum = 27*2/342 
                  = 0.16
Sulfur = (32*3)/342
           = 0.28
Oxygen = (16*12)/342
              = 0.56