Final answer:
The molecular formula of the compound with an empirical formula CH4 and a molar mass of 128 g/mol is C8H32, as the empirical formula mass fits 8 times into the molar mass.
Step-by-step explanation:
To determine the molecular formula from an empirical formula of CH4 when the molar mass is 128 g/mol, we first calculate the mass of the empirical formula. Carbon has an atomic mass of approximately 12 g/mol and hydrogen has an atomic mass of approximately 1 g/mol. Therefore, the empirical formula mass of CH4 is (12 + 4*1) = 16 g/mol.
To find out how many times the empirical mass fits into the molar mass, we divide the molar mass by the empirical formula mass: 128 g/mol / 16 g/mol = 8. This tells us that the empirical formula must be multiplied by 8 to get the molecular formula. The molecular formula is thus C8H32, which corresponds to option D.