Final answer:
The percent composition of carbon in octane (C8H18) is 84.1%, calculated by dividing the total molar mass of carbon in octane by the molar mass of octane and multiplying by 100.
Step-by-step explanation:
To calculate the percent composition of carbon in octane (C8H18), we need to determine the molar mass of octane and the molar mass of the carbon within it. The molar mass of carbon is approximately 12.01 g/mol, and hydrogen is about 1.008 g/mol. Since octane has 8 carbon atoms and 18 hydrogen atoms, we calculate the molar mass of octane as follows:
(8 × 12.01 g/mol C) + (18 × 1.008 g/mol H) = 96.08 g/mol C + 18.14 g/mol H = 114.22 g/mol for C8H18.
The percent of carbon is then calculated by the formula:
(Total mass of carbon / Molar mass of octane) × 100 = (96.08 g/mol / 114.22 g/mol) × 100 = 84.1%
Therefore, the percent composition of carbon in octane is 84.1%.