Understanding Empirical and Molecular Formulas

This page provides a comprehensive guide on how to calculate empirical formulas in chemistry and how to find molecular formula from empirical formula. It covers the key concepts and steps involved in determining these important chemical formulas.

The page begins by defining an empirical formula as one that gives the proportions of elements in a compound but not the actual numbers or arrangement of atoms. It then outlines a step-by-step process for calculating the empirical formula:

1. Convert percentages to grams, assuming 100g of the compound.
2. Calculate the number of moles for each element.
3. Divide each mole value by the smallest number of moles.
4. Round up or multiply to get whole numbers for the subscripts.

Definition: An empirical formula represents the simplest whole number ratio of atoms in a compound.

The page also explains that when dealing with carbon-containing compounds, if the numbers can't be rounded up easily, you may need to multiply until they become whole numbers. These numbers then become the subscripts in the formula.

Highlight: The molecular formula is described as the unsimplified version of the empirical formula, showing the actual number of atoms of each element in a molecule.

A detailed example is provided, demonstrating how to find empirical formula with percentages:

Example: For a compound with 48.64% Carbon, 8.16% Hydrogen, and 43.2% Oxygen:

1. Convert to grams: 48.64g C, 8.16g H, 43.2g O
2. Calculate moles: 4.05 mol C, 8.08 mol H, 2.7 mol O
3. Divide by smallest (2.7): 1.5 C, 3 H, 1 O
4. Multiply by 2 to get whole numbers: 3 C, 6 H, 2 O

This results in an empirical formula of C₃H₆O₂.

The page concludes by showing that to obtain the molecular formula, all subscripts in the empirical formula were multiplied by 2, resulting in C₆H₁₂O₄. This illustrates how to find molecular formula from empirical formula.

Vocabulary: Molar mass is used in these calculations and is defined as the mass of one mole of a substance, expressed in grams per mole (g/mol).

This comprehensive guide serves as an excellent resource for students learning about empirical and molecular formula practice problems, providing clear explanations and a practical example to reinforce understanding.