Final answer:
To calculate the percent composition by mass of hydrocarbon C9H20, you sum the atomic masses of the constituent atoms and then divide each element's total mass by the molecular mass. The result is 84.26% carbon and 15.74% hydrogen.
Step-by-step explanation:
To calculate the percent composition by mass of the hydrocarbon C9H20, you first need to know the atomic masses of carbon (C) and hydrogen (H). The atomic mass of carbon is approximately 12.01 amu (atomic mass units) and that of hydrogen is approximately 1.008 amu. For this hydrocarbon, the molecular mass can be calculated by adding the mass contributions from all the atoms: (9 atoms × 12.01 amu) + (20 atoms × 1.008 amu) = 108.09 amu + 20.16 amu = 128.25 amu.
Now, to find the percent composition for each element:
- Percent composition of carbon (C): (108.09 amu / 128.25 amu) × 100% = 84.26%
- Percent composition of hydrogen (H): (20.16 amu / 128.25 amu) × 100% = 15.74%
Therefore, the hydrocarbon C9H20 has a percent composition of 84.26% carbon and 15.74% hydrogen by mass.