Question

Explain the terms percentage composition, empirical formula, and molecular formula.

Answer 1

There are many ways to study the composition of a chemical compound which also includes percentage composition. It indicates the percentage by mass of each element in a compound.
Molecular formula and empirical formula are used to denote elements present in a compound. The former represents an exact number of atoms while the latter denotes the simplest ratio of atoms present.

Complete answer:
The percentage composition of a given compound is defined as the ratio of the amount of each element to the total amount of individual elements present in the compound multiplied by 100. It represents the composition of all elements present in a particular compound.
$\text{Percentage composition}=\dfrac{\text{Mass or amount of element present}}{\text{Total mass or amount of compound}}\times 100$
The percentage composition is used in chemical analysis to study the composition of any substance. To find the percentage composition, we need to know the molecular formula of the particular compound.
The molecular formula of a compound is the actual formula that specifies the exact number of atoms of each element present in a compound. Subscripts are used to denote the number of atoms. For example, the molecular formula of water is ${{\text{H}}_{\text{2}}}\text{O}$. It tells us each molecule has 2 hydrogen atoms and one oxygen atom.
There is another term used in chemical analysis known as the empirical formula. It is the simplest formula of a compound that represents the simplest ratio of elements present. If a compound's chemical formula cannot be reduced any more, then the empirical formula is the same as the chemical formula.
For example, the molecular formula of glucose is ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}$ and its empirical formula is $\text{C}{{\text{H}}_{\text{2}}}\text{O}$.

Additional information:
The oxidation numbers of each atom can find out using molecular formulas. We can also find out possible isomers, however, we cannot predict the exact molecular arrangement from molecular formula only.

Note:
The ionic compounds always have empirical formulas only. We cannot exactly tell how many atoms are present in a crystal of ionic compounds. So, we use the empirical formula for representing such compounds which denotes the relative ratio of atoms present.