What is the difference between empirical formula and molecular formula?
The empirical formula and molecular formula are both important concepts in chemistry that describe the composition of a substance. While they may seem similar, there are distinct differences between the two. Understanding these differences is crucial for accurately representing the composition of a chemical compound.
The empirical formula is the simplest whole number ratio of atoms present in a compound. It provides the relative proportions of different elements in a substance but does not indicate the actual number of atoms or the molecular mass. For example, the empirical formula of water is H2O, which indicates that the compound consists of two hydrogen atoms for every one oxygen atom. However, this formula does not specify the molecular mass or the actual number of atoms in a water molecule.
On the other hand, the molecular formula represents the actual number of atoms of each element present in a molecule of a compound. It provides both the relative proportions and the absolute number of atoms. The molecular formula is always a multiple of the empirical formula. Using the example of water, the molecular formula is also H2O, but it explicitly states that there are two hydrogen atoms and one oxygen atom in each water molecule.
One way to determine the molecular formula from the empirical formula is by knowing the molecular mass of the compound. By dividing the molecular mass by the empirical formula mass, we can find the whole number multiplier that gives us the molecular formula. For instance, if the molecular mass of a compound is 36 g/mol and the empirical formula is CH2O, we can calculate the molecular formula as follows:
Molecular mass / Empirical formula mass = Multiplier
36 g/mol / (12 g/mol + 2 g/mol + 16 g/mol) = 1.5
Since the multiplier is not a whole number, we need to multiply the empirical formula by 2 to obtain the molecular formula:
CH2O x 2 = C2H4O2
In summary, the key differences between the empirical formula and molecular formula are:
1. The empirical formula represents the simplest whole number ratio of atoms, while the molecular formula indicates the actual number of atoms in a molecule.
2. The empirical formula does not provide the molecular mass, whereas the molecular formula does.
3. The molecular formula is always a multiple of the empirical formula.
Understanding these differences is essential for chemists to accurately describe and represent the composition of chemical compounds.
