Question

What is a molecular formula? Explain its significance using potassium nitrate as an example.

Answer 1

Part-1: Definition of molecular formula

• A molecular formula is a chemical formula for a molecular compound that specifies the types and quantities of atoms in each molecule.
• The chemical elements are used to write the formula.
• For example, the formula of potassium nitrate is ${\mathrm{KNO}}_3$

Part-2: Significance

• The molecular formula is the formula derived from molecules and is representative of the total number of individual atoms present in a molecule of a compound.
• A molecular formula uses a subscript that reports the actual number of each type of atom in a molecule of the compound.
• Molecular formulas are associated with gram molecular masses that are simple whole number multiples of the corresponding empirical formula mass.

Example: Potassium nitrate (${\mathrm{KNO}}_3$):

• The molecule has combined with one potassium (K) atom, one nitrogen atom (N), and three oxygen atoms (O).
• They are present in the ratio 1:1:3
• The mass of one molecule of potassium nitrate is: $1\times (\mathrm{mass}\mathrm{of}\mathrm{potassium}\mathrm{atom})+1\times (\mathrm{mass}\mathrm{of}\mathrm{nitrogen}\mathrm{atom})+3\times (\mathrm{mass}\mathrm{of}\mathrm{oxygen}\mathrm{atom})$
• Let us plug in the values of atomic masses,
• $(1\mathrm{x}39\mathrm{u})+(1\mathrm{x}14\mathrm{u})+(3\mathrm{x}16\mathrm{u})=101\mathrm{u}.$

Hence, the molecular formula of potassium nitrate is ${\mathrm{KNO}}_3$ , and the molecular mass is101u.