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Topic 2: Amount of Substance
2.1: Relative atomic and molecular masses, the Avogadro
constant and the mole.
Relative atomic mass (Ar)

Definition: Relative atomic mass, Ar, is the weighted average mass of an atom of an
element, taking into account its naturally occurring isotopes, relative to 1/12th the relative

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Difference between this scale (based on H=1) and scale used today (based on
carbon12) is miniscule

The Mole

Definition: A mole is an amount of substance containing 6.022 x 10^23 particles.

Calculation: We must first know the substance's formula to find out how many moles are
present in the particular…

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The Empirical Formula

Definition: The formula that represents the simplest ratio of the atoms of each element
present in a compound.


Find the masses of each of the elements present in the compound.
Work out the number of moles of atoms of each element.
Use: Number…

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Number of moles in solution, n = M x V / 1000

2.5: Balanced equations and related calculations
Balanced symbol equations

Ionic equations

Strike out the spectator ions

Finding concentrations using titrations

Use: We carry out titrations to find the concentration of a solution, for example, an alkali. We


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