Emprical and Molecular Formula | Chemistry for Grade 11 (IGCSE) PDF Download

Calculating Empirical Formula 

• The empirical formula represents the simplest whole number ratio of atoms for each element in one molecule or formula unit of a compound. For instance, the empirical formula of ethanoic acid is CH₂O.
• Organic molecules may exhibit varying empirical and molecular formulae, illustrating different structural compositions.
• Notably, the formula of an ionic compound consistently aligns with an empirical formula.

Calculating Molecular Formula

• The molecular formula provides the precise numbers of atoms of each element found in the compound's formula.
• To calculate the molecular formula, follow these steps:
  • Determine the relative formula mass of the empirical formula.
  • Utilize the given equation:
    
  • Multiply the count of each element in the empirical formula by the derived value from step 2 to ascertain the molecular formula.

Table showing the Relationship between Empirical and Molecular Formula

Deducing formulae of hydrated salts

• The formula of hydrated salts can be established through experimental procedures.
• Initially, a sample of the hydrated salt is weighed, followed by heating it until all water of crystallization is removed.
• After this process, the anhydrous salt is reweighed, allowing the determination of both the mass of anhydrous salt and the mass of water of crystallization.
• Similar to deducing empirical formulas, these results enable the calculation of the hydrated salt's formula.