What is the approximate percent by mass of oxygen in SO_3?

• A. 60%
• B. 50%
• C. 80%
• D. 33%

Answer: (C)

Verified step by step guidance

1. Step 1: Identify the chemical formula and the elements involved. The compound is sulfur trioxide, SO_3, which contains sulfur (S) and oxygen (O).
2. Step 2: Find the atomic masses of sulfur and oxygen from the periodic table. Sulfur has an atomic mass of approximately 32 g/mol, and oxygen has an atomic mass of approximately 16 g/mol.
3. Step 3: Calculate the molar mass of SO_3 by adding the atomic mass of sulfur and three times the atomic mass of oxygen: \(M_{SO_3} = 32 + 3 \times 16\).
4. Step 4: Calculate the total mass of oxygen in one mole of SO_3, which is \$3 \times 16$ g.
5. Step 5: Calculate the percent by mass of oxygen in SO_3 using the formula: \(\text{Percent by mass of O} = \left( \frac{\text{mass of oxygen}}{\text{molar mass of } SO_3} \right) \times 100\%\).