C3 - Quantitative chemistry

• Law of conservation of mass

  No atoms are lost or made during a chemical reaction; mass of products equals mass of reactants
• Relative formula mass (Mr)


  Sum of the relative atomic masses of the atoms in the formula
• In a balanced chemical equation

  Sum of relative formula masses of reactants equals sum of products
• Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas
• Measurement uncertainty

  There is always some uncertainty about the result obtained
• Concentration of a solution

  • Measured in mass per given volume (g/dm3)
  • Can also be measured in mol/dm3
• Moles

  Chemical amounts measured in moles; 1 mole contains Avogadro's number of particles (6.02 x 10^23)
• The mass of one mole of a substance in grams is numerically equal to its relative formula mass
• Limiting reactant

  The reactant that is completely used up in a reaction
• Atom economy

  Measure of the amount of starting materials that end up as useful products
• Percentage yield is calculated by comparing the actual yield to the maximum theoretical yield
• Volume of gas

  Equal amounts in moles of gases occupy the same volume under the same conditions
• The volume of one mole of any gas at room temperature and pressure is 24 dm3
• Oxidation reactions

  Metals react with oxygen to produce metal oxides
• Chemical changes

  • Involves systematic experimentation and organization of results
  • Helps predict new substances formed