Question

Aluminum chlorohydrate, al2(oh)5cl, is an active ingredient in some antiperspirants. what is the mass percent of aluminum in this compound?

Answer 1

The percet of Al will be 100 times the mass of Al in the formula divided by the molar mass of the compound.

This table shows all the calculations involved

Compound: Al2 (OH)5 Cl

element     # of        atomic      mass in the          %
                  atoms    mass        formula
                                g/mol

Al              2             27             2*27 = 54 g        (54 / 174.5)*100 = 30.9%

O              5            16              5*16 = 80 g

H              5             1               5*1 =     5 g

Cl             1             35.5          1*35.5 = 35.5 g
                                              ----------------------
                   molar mass                      174.5 g

Answer: 30.9%