Final answer:
To find the percentage by mass of carbon in acetylene (C₂H₂), calculate the molar mass of the compound and use it to determine the mass percent of carbon, which is 92.3%.
Step-by-step explanation:
To calculate the percentage by mass of carbon in acetylene (C₂H₂), first, we need to determine the molar mass of the compound. The molar mass of carbon is about 12.01 g/mol and hydrogen is about 1.01 g/mol. Acetylene has two carbon atoms and two hydrogen atoms, so its molar mass is (2 × 12.01) + (2 × 1.01) = 26.04 g/mol.
Next, calculate the mass percent of carbon by taking the total mass of carbon in the formula (which is 2 × 12.01 g for the two carbon atoms) and dividing it by the molar mass of acetylene, then multiplying by 100 to get a percentage:
Percentage by mass of C = ((2 × 12.01 g/mol) / 26.04 g/mol) × 100% = 92.3%