Question: what is the percentage by mass of oxygen in al2 so4 3 2h2o?
Answer: The atomic masses of aluminum (Al), sulfur (S) and oxygen (O) are 27, 32 and 16, respectively. 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.