Fundamentals of Molar Mass and Stoichiometric Ratios

The mole is a set large number, known as Avogadro's number ( $6.022 \times 10^{23}$ ), used to scale individual atoms and molecules to measurable laboratory sample sizes.
Molar mass is defined as the mass in grams of one mole of a substance ( $\text{g/mol}$ ).
Elemental molar mass is found on the periodic table (e.g., Sulfur is $32.059\,\text{g/mol}$ ).

To convert from moles to mass: $\text{Mass (g)} = \text{moles} \times \text{molar mass}$ .
To convert from mass to moles: $\text{Moles} = \text{mass (g)} \times \frac{1}{\text{molar mass}}$ .
The molar mass serves as a conversion factor; users must pay attention to the given unit and the desired unit to orient the factor correctly.

The molar mass of a compound is the sum of the molar masses of its constituent elements, multiplied by their respective subscripts.
Example: One mole of $SO_2$ contains one mole of sulfur atoms and two moles of oxygen atoms.
Example: In $SCl_3$ , the molar mass is calculated by adding the molar mass of sulfur to three times the molar mass of chlorine.

The empirical formula is the most reduced molar ratio of elements in a fixed compound ratio.
Procedure to determine molar ratios from mass: 1. Convert each component's mass to moles using its specific molar mass. 2. Divide the number of moles of each component by the smallest number of moles present. 3. If necessary, multiply the results by a small whole number to achieve a whole-number ratio (e.g., finding the $2:1$ ratio for $H_2O$ ).
This method is used to determine the ratio between a compound and its waters of hydration in a hydrate (e.g., $\text{LiClO}_4 \cdot 3 H_2O$ ).