Question

A sample of potash alum K2SO4.Al2(SO4)3.24H2O contains 20 gram atoms oxygen in the sample, then calculate number of gram atoms of sulphur in the same sample

Answer 1

There are 40 O atoms in one formula unit, and 4 S atoms. As molar mass of Sulfur is 2 times larger then molar mass of Oxygen, then m(S) = $\frac{40\times4}{20\times2}=4 \ g.$