Question

Propylene has a molar mass of 42 grams and is composed of 85.7% carbon and 14.3% hydrogen, what is its molecular formula?

Answer 1

C3H6

Explanations:

Given the following parameters

%carbon = 85.7%

%Hydrogen = 14.3%

Convert percentage to mass

Mass of carbon = 85.7grams

Mass of Hydrogen = 14.3 grams

Convert mass to moles

Moles of Carbon = 85.7/12 = 7.142moles

Moles of Hydrogen = 14.3/1 = 14.3 moles

Divide by the lowest ratio

For Carbon: 7.142/7.142 = 1

For Hydrogen: 14.3/7.142 = 2.002

Determine the empirical formula

Empirical formula = CH2

Determine the molecular formula

(Empirical formula)n = molar mass of Propylene

(CH2)n = 42

(12 + 2(1))n = 42

14n = 42

n = 42/14

n = 3

Molecular formula = (CH2)3 = C3H6

Therefore the molecular formula of propylene is C3H6