6.6- Empirical to Molecular formula

On this page, we will learn how to solve problems like these:

 

'Determine the molecular formula of a compound with

the empirical formula CF2 and a molar mass of 200.04 g/mol'

 

What is a molecular formula?

- a formula giving the number of atoms (moles) of each of the elements present in one molecule of a specific compound.

e.g    Mg3N2  is the empirical formula because its the smallest value of ratio between the two elements

      Mg6N4 is the molecular formula. It has the same ratio, just in a multiple. It would be according to the            compound/ molar mass

 

By looking back at the question, we can represent the information through a chart.

 

Multiple   Formula   Molar mass 

                   CF2                      50.01    

    x2           C2F4            100.02

    x3           C3F6            150.03

    x4           C4F8           200.04  <--- you can see here, that this value, is the same value as the                                                                question given. 200.04 g/mol

 

Therefore, the correct molecular formula that answers this question, is  C4F8 

 

This table shows you clearly how the atoms work throughout the calculating process.

BUT, we simply can't be using this method to solve every single question. 

 

Don't worry, there's an easier way. 

 

what we multiply by:                           molar mass of 

                                                   molecular formula

                                                      molar mass of 

                                                    empirical formula

 

 

In this same question:

 

200.04 

50.01

 

 

= 4

 So we can say that:

          x4

50.01--->200.04

 

we can use the same multiplication to multiply with the empirical formula:

          x4

CF2--->C4F8

 

It's that easy!

 

 

 

 

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