Empirical formula — Science definition
Simplest whole-number atom ratio.
Where it is taught
- Percent Composition, Empirical & Molecular Formulas — Reactions, Moles & Composition, Physical Science: Chemistry, Grade 11
In use
An empirical formula gives the simplest whole-number atom ratio.
Percent Composition, Empirical & Molecular Formulas
Questions using empirical formula
Problem 1
An empirical formula mass is 15 g/mol and the molecular molar mass is 60 g/mol. Find the subscript multiplier.
Hints
List the given quantities, select a relationship, and check units before substituting.
Answer and explanation
4
60/15=4.
Problem 2
An empirical formula is CH₂O, mass 30 g/mol; measured molar mass is 90 g/mol. Find molecular formula. Show the reasoning, not just the conclusion.
Hints
Percentages describe mass, so convert to moles before atom ratios.
Answer and explanation
90/30=3; multiply subscripts to get C₃H₆O₃.
Problem 3
A compound has molar masses 24 g of C and 4 g of H in the analyzed portion. Use C=12 and H=1 to find empirical formula.
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Moles C=2, H=4; ratio 1:2, giving CH₂.
Problem 4
Simplify C₄H₈ to its empirical formula.
Answer and explanation
CH₂: divide both subscripts by 4.
Response criteria
- State a scientifically accurate conclusion.
- Show the calculation or mechanism that supports it.
- Include units, conditions, or limits where relevant.