Question

If an unknown compound is found to have an empirical formula of CH4, which of the following is the molecular formula if the molar mass was determined to be 128 g/mol?

A. CH4
B. CH12
C. C8H12
D. C8H32
E. C12H16

Answer 1

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.