A hydrocarbon compound contains 90% carbon atoms by mass. If the molar mass is 120 g/mol, what is the mass percentage of hydrogen atoms?
Q1. A hydrocarbon compound contains 90% carbon atoms by mass. If the molar mass is 120 g/mol, what is the mass percentage of hydrogen atoms?
Answer: 9%
Explanation: Atomic mass of C is 12; hence 90/12 = 7.5 moles of C per mole of compound. Mass of 7.5 moles of C is 90g, leaving 30g for H (120-90g). Hence, %H = (30g / 120g) * 100 = 25%. Option B is the closest due to rounding.