What is the percent by mass of sulfur in aluminum sulfate (Al_2(SO_4)_3)?

• A. 35.0%
• B. 18.7%
• C. 28.1%
• D. 12.5%

Answer: (B)

Verified step by step guidance

1. Identify the chemical formula of aluminum sulfate: \(\mathrm{Al_2(SO_4)_3}\).
2. Calculate the molar mass of aluminum sulfate by summing the atomic masses of all atoms in the formula: 2 aluminum (Al), 3 sulfur (S), and 12 oxygen (O) atoms. Use the atomic masses: \(\mathrm{Al} = 26.98\,g/mol\), \(\mathrm{S} = 32.07\,g/mol\), and \(\mathrm{O} = 16.00\,g/mol\).
3. Calculate the total mass contributed by sulfur atoms: multiply the number of sulfur atoms (3) by the atomic mass of sulfur (\$32.07\,g/mol$).
4. Calculate the percent by mass of sulfur in aluminum sulfate using the formula: \(\%\,\mathrm{S} = \left( \frac{\text{mass of sulfur}}{\text{molar mass of aluminum sulfate}} \right) \times 100\%\).
5. Substitute the values from previous steps into the formula and simplify to find the percent by mass of sulfur.