Quantitative chemistry

• The conservation of mass means that the total mass of the reactants is equal to the total mass of the products in a chemical reaction
• Balancing symbol equations


  1. Decrease in mass

  2. Increase in mass
• When writing symbol equations, you need to ensure that the number of each atom on each side is equal
• State symbols


  • Solid (s)
  • Liquid (l)
  • Gas (g)
  • Aqueous or dissolved in water (aq)
• Ratio


  The balanced ratio of the reactants and products in a chemical reaction
• Formula mass


  The sum of the relative atomic masses of all the atoms in a substance
• Avogadro constant


  One mole of a substance contains 6.02 x 10^23 atoms, ions, or molecules
• One mole of a substance has the same mass as the formula mass of the substance
• Using balanced equations


  1. Balance the symbol equation

  2. Calculate moles of the substance with a known mass

  3. Using the balanced symbol equation, work out the number of moles of the unknown substance

  4. Calculate the mass of the unknown substance using mass = moles x formula mass
• Excess and limiting reactants


  The reactant that runs out is the limiting reactant, the other reactant is in excess
• Balancing an equation


  1. Work out the formula mass of all the substances

  2. Calculate the number of moles of each substance in the reaction using moles = mass/formula mass

  3. Convert to a whole number ratio

  4. Balance the symbol equation
• Concentration


  The amount of solute in a volume of solvent
• Examiners like to ask questions that bring together ideas from different places