The atomic mass of carbon (C) is 12.011 amu, and the atomic mass of hydrogen (H) is 1.008 amu. Which substance has a molar mass of 42.081 g/mol?
a) C₃H₆
b) C₂H₄
c) C₂H₆
d) C₃H₈
To find the molar mass of the substance, multiply the atomic masses of carbon and hydrogen by the number of atoms in the given formula:
a) C₃H₆: (3 * 12.011) + (6 * 1.008) = 36.033 + 6.048 = 42.081 g/mol
b) C₂H₄: (2 * 12.011) + (4 * 1.008) = 24.022 + 4.032 = 28.054 g/mol
c) C₂H₆: (2 * 12.011) + (6 * 1.008) = 24.022 + 6.048 = 30.070 g/mol
d) C₃H₈: (3 * 12.011) + (8 * 1.008) = 36.033 + 8.064 = 44.097 g/mol
The substance with a molar mass of 42.081 g/mol is C₃H₆, so the answer is (a) C₃H₆.