The empirical formula of a hydrocarbon with a molar mass of 78.11g/mol is CH. What is the molecular formula? show your work please.

Question

Answer choices are

a) C6H6

b) C5H28

c) C5H2O

d) C2H4

e) C8H18

Answer 1

On this type of question, first you want to determine the molar mass of the given empirical formula CH

Molar Mass of CH = 12.01 g/mol + 1.01 g/mol = 13.02 g/mol

From there then you can determine the subscript amounts by finding what the ratio "n" is

78.11 g / 13.02 g/mol = 6

Meaning that the molecular formula here is

C6H6

Answer 2

To solve this problem, you need to start by find the molar mass of the empirical formula, CH. 

 

C = 12.01 g

H = 1.008 g

 

So CH = 13.018 g

 

Now you need to divide the molar mass of the compound by the molar mass of the empirical formula.  That will tell you which multiple is correct.

 

78.11/13.018 = 6

 

So the molecular formula is the sixth multiple of the empirical formula.  Simply multiply the subscripts of the empirical formula (CH) by 6, and you have your answer.