Lecture Notes on Molar Mass and Conversions

Introduction to Molar Mass

Molar Mass: The mass of one mole of a substance, expressed in grams per mole (g/mol).
Useful for converting between grams and moles.
Often referred to as: molecular weight, formula weight, formula mass, molecular mass.
Fundamental in general chemistry for understanding reactions and stoichiometry.

Provides a basis for comparing different substances through moles.
Moles represent the number of entities (atoms, molecules) reacting, not mass.
Molar mass helps identify unknown substances by calculating from given mass to moles.

Ammonium Nitrate (NH₄NO₃):
- Components: 2 Nitrogen (N), 4 Hydrogen (H), 3 Oxygen (O).
- Atomic masses: N = 14.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol.
- Calculated molar mass: 80.05 g/mol (rounded to correct significant figures).
Calcium Permanganate (Ca(MnO₄)₂):
- Components: 1 Calcium (Ca), 2 Manganese (Mn), 8 Oxygen (O).
- Atomic masses: Ca = 40.08 g/mol, Mn = 54.94 g/mol, O = 16.00 g/mol.
- Calculated molar mass: 278.0 g/mol (rounded to correct significant figures).

Grams to Moles Conversion:
- Example: 25 grams of Carbon (C).
- Atomic mass of Carbon: 12.01 g/mol.
- Calculation: 25 g ÷ 12.01 g/mol = 2.08 moles.
Grams to Atoms Conversion:
- Example: 675 grams of Iron (Fe).
- Atomic mass of Iron: 55.85 g/mol.
- Use Avogadro's number for conversion: 6.022 × 10²³ atoms/mole.
- Calculation: (675 g ÷ 55.85 g/mol) × 6.022 × 10²³ = 7.28 × 10²⁴ iron atoms.
Grams to Molecules Conversion:
- Example: 675 grams of Water (H₂O).
- Molar mass of Water: 18.02 g/mol.
- Use Avogadro's number: 6.022 × 10²³ molecules/mole.
- Calculation: (675 g ÷ 18.02 g/mol) × 6.022 × 10²³ = 2.26 × 10²⁵ water molecules.

Always use the periodic table to find atomic masses for calculations.
Pay attention to significant figures during conversions.
Ensure logical consistency (e.g., larger amounts should result in larger numbers of atoms/molecules).
Use molar mass to identify and analyze chemical species.