Empirical formula question?

In 7.2 g of the hydrocarbon:
Mass of C = 6.0 g
Mass of H = (7.2 - 6.0) g = 1.2 g

Mole ratio C : H
= (6.0/12) : (1.2/1)
= 0.5 : 0.6
= 5 : 6

The empirical formula = C₅H₆

7.2 g total - 6.0 g C = 1.2 g H

(6.0 g C) / (12.01078 g C/mol) = 0.49955 mol C

(1.2 g H) / (1.007947 g H/mol) = 1.19054 mol H

Divide by the smaller number of moles:
(0.49955 mol C) / 0.49955 mol = 1.000000
(1.19054 mol H) / 0.49955 mol = 2.383225

In order to achieve integer coefficients multiply by 8, then round to the nearest whole numbers to find an empirical formula:
C8H19
However, it is not possible to have a hydrocarbon with more than 18 hydrogen atoms when there are 8 carbon atoms.  So try the next best multiple for achieving integers, which is 5:
C5H12
This is a reasonable formula for a hydrocarbon -- and an alkane in particular -- so it is the answer to this question.

The answer you were given contains a mistake. Here's the offending portion:

Mole ratio C : H= (6.0/12) : (1.2/1)= 0.5 : 0.6= 5 : 6

-------------------------

The error is in this:

(1.2/1)

The answer is 1.2 and not the 0.6 given in the next line of the answer.

When corrected, this part of the answer looks like this:

Mole ratio C : H= (6.0/12) : (1.2/1)= 0.5 : 1.2= 5 : 12

Which given an empirical formula of C5H12.

The poster of the answer may edit their answer to correct the mistake.

Since it is a hydrocarbon, it contains only the elements of carbon & hydrogen 
6.0g of carbon and 1.2 g of hydrogen  6.0 + 1.2 = 7.2 g
For each element divide by its atomic mass. 
C ; 6.0 /12 = 0.5 
H ; 1.2 / 1 = 1.2 
Now ratio each element 
C:H :: 0.5 : 1.2 :: 1 : 2.4
Since we don't like decimals in the ratios, we multiply up to remove the decimal. In this case by '5'. 
C:H :: 1: 2.4 :: 5 : 12  is the ratio of 'C' to 'H' 
Hence empirical formula is C5H12 .

This formula could be the molecular formula for the  alkane Pentane (C5H12 ). 
 

This used to be a respectful place to exchange chemistry solutions 

Now it is inhabited by belligerent post docs calling people names and harassing the questionners.

If he's so smart why is he hanging around ?