A sample of a certain organic acid has a mass of 5.000 g. Elemental analysis of this compound found it to contain 1.334 g C, 3.554 g O, and the rest of the mass is hydrogen. If the molar mass of the organic acid is 90.03 g/mol, determine its molecular formula.

C₂H₂O₄

Explanation:

Given parameters:

Mass of organic acid  = 5g

Mass of C  = 1.334g

Mass of O = 3.554g

Mass of H = 5  - (1.334 + 3.554)  = 0.112g

Molar mass  = 90.03g/mol

Unknown:

Molecular formula of the compound  = ?

Solution:

To solve this problem, we find the empirical formula of the compound first. It is the simplest formula of the compound.

Elements                        C                     H                        O

Mass                             1.334               0.112                   3.554

Molar mass                       12                   1                          16

Number of moles          1.334/12          0.112/1                 3.554/16

                                         0.112              0.112                     0.222

Divide by the

Smallest                         0.112/0.112        0.112/0.112          0.222/0.112

                                                1                       1                      2

           Empirical formula  = CHO₂  

The molar mass of this empirical formula  = 12 + 1 + 2(16) = 45g/mol

Now;

  Multiplication index  =    = 2

Molecular formula  =  (CHO₂)₂    = C₂H₂O₄  

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