Formulae
Key definitions
- Molecular formula — the number and types of different atoms in one molecule.
- Empirical formula — the simplest whole number ratio of different atoms or ions in a compound.
Writing ionic equations
- Write out the full equation, including states.
- Split all aqueous compounds into its ions.
- Cross out any spectator ions (ions that are in both products and reactants).
- Rewrite your final equation!
To know if a compound is aqueous, refer to the solubility chart (chp 7).
All acids are aqueous.
Relative masses of atoms and molecules
Relative molecular mass — the sum of the relative atomic masses of all atoms in a molecule.
- Relative atomic mass — the average mass of isotopes of an element in comparison to 1/12th of a mass of carbon-12.
The mole and the Avogadro constant
- Mole — the unit of amount of substance where one mole contains 6.02 x 10^23 particles.
- Avogadro's constant — 6.02 x 10^23.
Concentration is in g/dm3 or mol/dm3.
Other experimental formulas
- Percentage yield — (Actual mass obtained / theoretical mass) x 100
- Percentage purity or composition by mass — (Mass of key substance / Mass of total substance) x 100