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    Quantitative Chemistry

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    Lesson step 1 of 4Relative Masses & Moles

    Relative Masses & Moles

    Relative atomic mass (Ar) is the weighted average mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12.

    Relative formula mass (Mr) is found by adding up the Ar values of all atoms in the formula.

    Example: H2SO4 → Mr = (2 × 1) + 32 + (4 × 16) = 98

    (Higher) One mole of any substance contains 6.02 × 1023 particles (Avogadro's constant). The mass of one mole equals the Mr in grams.

    (Higher) Moles = massMr

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    Key Terms

    Mole
    The amount of substance containing 6.02 × 10²³ particles; mass equals the Mr in grams.
    Concentration
    The amount of solute dissolved in a given volume of solution (mol/dm³ or g/dm³).
    Atom economy
    The percentage of reactant atoms that form the desired product.