10. Mole Concept
Definitions
State Symbols
Formulae for Calculations
Click here to download a FREE Formula Sheet for Mole Calculation.
Limiting Reactants
- Relative atomic mass, Ar: The relative atomic mass of an atom is the average mass of an atom of an element compared to 1/12 the mass of an atom of carbon-12.
- Relative molecular mass, Mr: The relative molecular mass of a molecule is the average mass of one molecule of a compound compared to 1/12 the mass of an atom of carbon-12.
- Empirical formula: Simplest formula showing the ratio of the atoms of each element in one molecule of a compound.
- Molecular formula: The formula showing the actual number of the atoms of each element in one molecule of a compound.
State Symbols
- s – solid (e.g. solid copper(II) chloride contains Cu2+ and Cl- ions in fixed positions)
- l – liquid / molten (e.g. liquid/molten copper(II) chloride contains only mobile Cu2+ and Cl- ions)
- g – gas ( i.e. carbon dioxide molecules which are far apart and in rapid, random movement)
- aq – aqueous (i.e copper(II) chloride solution contains Cu2+, Cl-, H+, OH-)
- Ar - from Periodic Table
- Mr - sum of Ar in formula
- Mr (no units) is numerically equal to molar mass (g/mol)
- For gases only, mole ratio is equivalent to volume ratio. One mole of any gas occupies the same volume (24 dm3).
- Calculation on concentration of solutions: The concentration of a solution gives the amount of solute in 1 dm3 of solution. It can be expressed in g/cm3 or mol/dm3.
Formulae for Calculations
Click here to download a FREE Formula Sheet for Mole Calculation.
Limiting Reactants
- A balanced chemical equation is used to calculate the exact amount of reactants used up and products formed using its mole ratio.
- The reactant that is completely used up is known as the limiting reactant. It determines or limits the amount of product formed.
- Once the limiting reactant is used up, the reaction stops.
- Always use the limiting reactant to calculate the product.
