8.4

Molecular Formulas: Vocabulary and molecular formulas from empirical formulas and molar mass

Molar mass of the molecular compound

The additional piece of information required to solve for a molecular formula when the empirical formula is known.

Mass conversion assumption

To convert percentages of elements to grams, assume a $100\,g$ sample and change the percent signs to grams.

Empirical Formula

Shows the reduced ratio of elements (e.g., the empirical formula of hydrogen peroxide is HO)

Molecular Formula

Shows the exact, real-world quantity of atoms per molecule (e.g., the molecular formula of hydrogen peroxide is H₂O₂).

Which formula must always be found first?

The empirical formula must always be determined first before using molar mass to find the molecular formula.

What information is needed to determine a molecular formula?

• Empirical formula

• Molar mass of the compound

Molecular Mass Formula

$Molecular Mass =$ $</p><p>\Sigma\left(Atomic\right.Mass$

$x$ $NumberOfAtoms)$