Question

A certain hydrocarbon is 85.7 % carbon and 14.3 % hydrogen by mass.

a) What is the empirical formula of the hydrocarbon? Be sure to write the carbon first.

_______

b) If the molar mass of the hydrocarbon is approximately 40 g/mol, what is its molecular formula? Be sure to write carbon first.

________

Answer 1

A)

C moles = 85.7 / 12 = 7.14

H moles = 14.3 / 1 = 14.3

moles ration = C : H = 7.14 : 14.3 = 1 : 2

empirical formula = CH2

b)

CH2 mass = 12 + 2 = 14

molar mass =40

n = 40 / 14 = 2.9 nearly 3

molecular formula = n x empirical formula

                              = 3 x CH2

                             = C3H6