Question

What is the empirical formula of Caffeine $({{C}_{8}}{{H}_{10}}{{N}_{4}}{{O}_{2}})$, a substance found in tea and coffee?

Answer 1

The empirical formula of any compound can be calculated easily using the following formula.
$\text{Molecular formula = n}\times \text{empirical formula}$
In order to use this formula, we must be knowing either molecular formula or empirical formula.

Complete step by step solution:
- Empirical formula is the simplest formula which provides the lowest whole number ratio of the element present in the compound.
- Relative Number of all the elements present in the compound can be found using the empirical formula.
- Empirical formula can be calculated using this formula
$\text{Molecular formula = n}\times \text{empirical formula}$
- Molecular formula is the multiple of the empirical formula.
- Molecular formula gives the actual number of elements present in the compound.
For example, in acetylene:
-${{C}_{2}}{{H}_{2}}$is the molecular formula and $CH$is the empirical formula.
For caffeine, the molecular formula is $({{C}_{8}}{{H}_{10}}{{N}_{4}}{{O}_{2}})$
Using the formula, Molecular formula = n. empirical formula
where n is taken as the lowest number of elements present in the compound.
Oxygen atoms are present in the lowest quantity. So, n is taken as 2.
${{\text{C}}_{8}}{{\text{H}}_{10}}{{\text{N}}_{4}}{{\text{O}}_{2}}\text{ = 2 }\times \text{ Empirical formula}$
$\text{Empirical formula =}\dfrac{{{C}_{8}}{{H}_{10}}{{N}_{4}}{{O}_{2}}}{2}$
$\text{Empirical formula = }{{\text{C}}_{4}}{{\text{H}}_{5}}{{\text{N}}_{2}}\text{O}$

Therefore, empirical formula of caffeine is ${{\text{C}}_{4}}{{\text{H}}_{5}}{{\text{N}}_{2}}\text{O}$.

Additional information:
-Caffeine is Methylxanthine alkaloid. It is found in coffee seeds, tea leaves, nuts, etc.
- Its IUPAC name is $1,3,7-Trimethylpurine-2,6-dione$.
- It is a stimulant for the central nervous system.

Note: -Empirical formula and molecular formula are different from each other.
- Molecular formula gives actual number of elements present in the compound whereas empirical formula gives lowest whole number ratio of the element present in the compound.