The empirical formula, CH2, has a relative molecular mass of
1×(12.01)+2×(1.01)=14.04
This means that the empirical formula must be multiplied by a factor to bring up its molecular weight to 70. This factor can be calculated as the ratio of the relative masses of the molecular and empirical formulas
7014.04=4.98≈5
Remember that subscripts in molecular formulas must be in whole numbers, hence the rounding-off. Finally, the molecular formula is
C1×5H2×5=C5H10
