Question

In science class, students are learning about organic compounds. An acetic acid molecule is made of 2 carbon atoms, 2 oxygen atoms and 4 hydrogen atoms. What is the ratio of carbon atoms and hydrogen atoms

Answer 1

The simplest ratio of elements in a molecule is called as Empirical Formula. 
For Example,
Empirical formula of Benzene is CH
Empirical formula of Formaldehyde is CH₂O

Calculation of Empirical Formula:
Empirical formula can be calculated from Molecular formula by dividing the molecular formula with such number that all number of elements in molecular formula gets the lowest and simplest number.
Like Benzene Molecular formula is C₆H₆, when it is divided by 6 we get C₁H₁ or simply CH.
So, for acetic acid having molecular formula C₂H₄O₂ we can only divide it with 2 to have the simplest form, i.e.
C₂H₄O₂ ÷ 2 = C₁H₂O₁ or CH₂O

Result:
So the ratio of elements in acetic acid is

                                          C : H : O
                                           1 : 2 : 1