Question

The percent composition by mass of oxygen in $BaS{O}_4$ is :

• A. $233.4$%
• B. $66.7$%
• C. $27.4$%
• D. $58.7$%
• E. $13.7$%

Answer 1

Answer: (C)

$27.4$%

The percent composition by mass of oxygen in $BaS{O}_4$ is $27.4$.
The atomic masses of $Ba,S$ and $O$ are 137.3 g/mol, 32.1 g/mol and 16 g/mol respectively. The molar mass of $BaS{O}_4$ is $137.3+32.1+4\left(16\right)=233.4$ g/mol
The percent composition by mass of oxygen in $BaS{O}_4$ is $\frac{100\times 4\left(16\right)}{233.4}=27.4$ %.