Calculate the percentage of oxygen in Al2(SO4)3?  

Expert Answers
gsenviro eNotes educator| Certified Educator

To calculate the percentage of oxygen in aluminum sulfate, `Al_2(SO_4)_3`  , we need to determine the molar mass of this salt. The atomic masses of aluminum (Al), sulfur (S) and oxygen (O) are 27, 32 and 16, respectively.

Thus, the molar mass of aluminum sulfate = 2 x 27 + 3 x 32 + 4 x 3 x 16

= 342 gm/mole

The mass contributed by oxygen = 4 x 3 x 16 = 192 gm

% contribution of oxygen = mass of oxygen x 100/ mass of aluminum sulfate

= 192/342 x 100 = 56.14%

Thus, oxygen contributes about 56% of mass to aluminum sulfate. Similarly, sulfur contributes 28.1% (96/342 x 100) and aluminum contributes 15.8% to the total mass of aluminum sulfate. 

This salt is generally sold as alum and is used as a coagulating agent in water treatment process.

Hope this helps.