1. Understand Empirical Formulas
* An empirical formula shows the simplest whole-number ratio of atoms in a compound. It doesn't tell you the exact number of atoms in a molecule.
2. Information You Need
* Percent Composition: You need the percentages by mass of each element in mandelic acid. This is typically provided in the problem.
* Atomic Masses: You'll need the atomic masses of each element from the periodic table.
3. Example (Let's assume the following percent composition for mandelic acid):
* Carbon (C): 63.15%
* Hydrogen (H): 5.30%
* Oxygen (O): 31.55%
4. Calculations
* Assume 100 g of Mandelic Acid: This makes the percentages directly equivalent to grams.
* Convert Grams to Moles: Divide the mass of each element by its atomic mass:
* Carbon: 63.15 g / 12.01 g/mol = 5.26 mol C
* Hydrogen: 5.30 g / 1.01 g/mol = 5.25 mol H
* Oxygen: 31.55 g / 16.00 g/mol = 1.97 mol O
* Find the Simplest Ratio: Divide each mole value by the smallest mole value:
* Carbon: 5.26 mol / 1.97 mol = 2.67 ≈ 2.7
* Hydrogen: 5.25 mol / 1.97 mol = 2.67 ≈ 2.7
* Oxygen: 1.97 mol / 1.97 mol = 1
* Adjust to Whole Numbers: Since we have close to 2.7, we can multiply all values by 3 to get whole numbers.
* Carbon: 2.7 x 3 = 8
* Hydrogen: 2.7 x 3 = 8
* Oxygen: 1 x 3 = 3
5. Empirical Formula
The empirical formula for mandelic acid is C₈H₈O₃.
Note: This is only the empirical formula. The actual molecular formula for mandelic acid is C₈H₈O₃, which happens to be the same as the empirical formula.
