Overview
This lecture covers how to calculate molar mass, use molar mass as a conversion factor between grams, moles, molecules, and atoms, and solve stoichiometric problems involving compounds like propanol, calcium nitrate, and sulfuric acid.
Calculating Molar Mass
- Molar mass is the mass of one mole of a substance, calculated using the periodic table.
- To find molar mass, sum the masses of each element in the compound multiplied by the number of atoms present.
- Example: One mole of propanol (C₃H₈O) contains 3 moles C, 8 moles H, and 1 mole O.
- Use atomic masses (e.g., C = 12.011 g/mol) multiplied by the number of atoms, then add together for total molar mass.
Using Molar Mass in Conversions
- To convert moles to grams: multiply moles by the compound's molar mass.
- To convert grams to moles: divide grams by the compound's molar mass.
- Example: 0.25 moles of propanol × 60.0956 g/mol = 15 g propanol.
- Example: 1.2 g propanol ÷ 60.0956 g/mol = 0.01996 moles of propanol.
Handling Polyatomic Compounds
- For compounds like calcium nitrate, apply the distributive property for groups in parentheses.
- Example: Ca(NO₃)₂ contains 1 Ca, 2 N, and 6 O atoms per formula unit.
- Calculate molar mass using atomic weights and numbers of atoms.
Molecules and Atoms Calculations
- To convert grams to molecules: go from grams → moles → molecules using Avogadro’s number (6.022 × 10²³).
- To find atoms (e.g., C in propanol): go from grams → moles (compound) → moles (element) → atoms (element).
- Example: 1.2 g propanol contains 3.607 × 10²² atoms of carbon.
Nanograms Calculation and Dimensional Analysis
- To convert between molecules and nanograms: molecules → moles → grams → nanograms (1 ng = 10⁻⁹ g).
- Example: 9.24 × 10¹⁴ molecules H₂SO₄ equals 150 nanograms.
Key Terms & Definitions
- Mole — the amount of substance containing 6.022 × 10²³ entities (Avogadro’s number).
- Molar Mass — the mass in grams of one mole of a substance.
- Avogadro’s Number — 6.022 × 10²³, the number of particles in a mole.
- Dimensional Analysis — a method to convert between units using conversion factors.
Action Items / Next Steps
- Practice calculating molar masses for assigned compounds.
- Complete conversion exercises between grams, moles, molecules, and atoms as homework.
- Review periodic table atomic masses for accuracy in calculations.