Final answer:
To determine the percent composition of aspirin (C9H8O4), the molecular mass of 180.15 amu is calculated by adding the atomic masses of carbon, hydrogen, and oxygen. The percent composition is found by dividing the mass contribution of each element by the total molecular mass and multiplying by 100.
Step-by-step explanation:
To calculate the percent composition of aspirin, which has the molecular formula C9H8O4, we first determine the molecular mass of aspirin. The molecular mass is the sum of the atomic masses of each atom in the molecule. Aspirin consists of nine carbon atoms (C), eight hydrogen atoms (H), and four oxygen atoms (O). The atomic mass of carbon is approximately 12.01 atomic mass units (amu), hydrogen is about 1.008 amu, and oxygen is 16.00 amu. Multiplying the atomic masses by the number of each type of atom and summing them gives us the total molecular mass of aspirin:
- Carbon: 9 atoms × 12.01 amu = 108.09 amu
- Hydrogen: 8 atoms × 1.008 amu = 8.064 amu
- Oxygen: 4 atoms × 16.00 amu = 64 amu
The molecular mass of aspirin is therefore 108.09 amu + 8.064 amu + 64 amu = 180.15 amu.
To find the percent composition, divide the mass contribution of each element by the total molecular mass and multiply by 100:
- Percent composition of carbon in aspirin = (108.09 amu / 180.15 amu) × 100
- Percent composition of hydrogen in aspirin = (8.064 amu / 180.15 amu) × 100
- Percent composition of oxygen in aspirin = (64 amu / 180.15 amu) × 100