General Chemistry: Percentage Composition

Vocabulary flashcards covering key terms, formulas, and step-by-step percentage composition examples from the lecture.

Percentage Composition

The percentage by mass of each element in a compound.

Atomic Mass

The mass of one atom of an element.

Subscript

A number in a chemical formula showing how many atoms of each element are present.

Molar Mass

The mass of $1$ mole of a compound, calculated as the sum of all atomic masses in the chemical formula.

Percentage Mass Formula

$$\text{\% Mass of Element} = \frac{\text{Total mass of element in compound}}{\text{Molar mass of compound}} \times 100$$

Subscript Multiplier Rule for Parentheses

To find the total number of atoms for an element inside parentheses (e.g., $(\text{NO}_3)_2$), multiply the atom count inside the parentheses by the subscript outside.

Percentage Composition Table for Water (H2O)

A table detailing the elements in $\text{H}_2\text{O}$: 2 H atoms ($2.02\,g\,mol^{-1}$, $11.21\%$) and 1 O atom ($16.00\,g\,mol^{-1}$, $88.79\%$), adding up to a molar mass of $18.02\,g\,mol^{-1}$ ($100\%$).

Percentage Composition Table for Magnesium Nitrate

A table detailing the elements in $\text{Mg(NO}_3\text{)}_2$: 1 Mg atom ($24.31$ mass, $16.39\%$), 2 N atoms ($28.02$ mass, $18.89\%$), and 6 O atoms ($96$ mass, $64.72\%$), adding up to a total molar mass of $148.33$ ($100\%$).