Unit 1.1: Moles and Molar Mass

Apply Avogadro’s number to calculate the number of moles given the number of particles in a substance and vice versa.

  1. How many moles are in 3.01 × 10²³ molecules of CO₂?
    0.50 mol CO₂ (since 3.01 × 10²³ is half of Avogadro’s number).

Understand that the mass of a single atom in amu is equal to the mass of a mole of that substance in grams.

  1. The mass of a carbon atom is 12 amu. What is the mass of one mole of carbon atoms in grams?
    12 grams (1 amu per atom corresponds to g/mol on the molar scale).

Use molar mass to convert between mass and moles of a substance.

  1. How many moles are in 25.0 g of H₂O?
    25.0 g ÷ 18.0 g/mol = 1.39 mol H₂O.

Use subscripts to convert between molecules and the number of atoms of a given element.

  1. How many hydrogen atoms are in 2.0 moles of NH₃?
    2.0 mol × 6.022 × 10²³ molecules/mol × 3 H per molecule = 3.61 × 10²⁴ H atoms.
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