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Question

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


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Solution

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 KNO3

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 (KNO3):

  • 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×(massofpotassiumatom)+1×(massofnitrogenatom)+3×(massofoxygenatom)
  • Let us plug in the values of atomic masses,
  • (1x39u)+(1x14u)+(3x16u)=101u.

Hence, the molecular formula of potassium nitrate is KNO3 , and the molecular mass is101u.


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