If a compound has a molar mass of 70.13 g/mol and its empirical formula is CH2, what is its molecular formula

The molecular formula is ALWAYS, a whole number multiple of the empirical formulaand of course the multiple might be one...

And so we can write

{empirical formula}n=molecular formula

And taking the given molecular mass of 70.13⋅g⋅mol−1

n=70.13⋅g⋅mol^−1/(12.011+1.00794×2)⋅g⋅mol−1=5

And so

{CH2}×5=C5H10