quantitative chemistry

• Mole


  The unit used to measure chemical amounts
• Mole

  • The mass of one mole of a substance in grams is numerically equal to its relative formula mass
  • One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance
• Converting between moles and grams

  Use the triangle or the equation: mass = moles x molar mass (may need to rearrange)
• The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant: 6.02 x 10^23 per mole
• Balanced symbol equation

  Can be interpreted in terms of moles
• The total moles of one element must be the same on both sides of the equation
• Balancing numbers in a symbol equation

  1. Convert the masses in grams to amounts in moles

  2. Convert the numbers of moles to simple whole number ratios
• Limiting reactant


  The reactant that is used up / not in excess (since it limits the amount of products)
• If a limiting reactant is used, the amount of product produced is restricted to the amount of the excess reactant that reacts with the limiting one
• Concentration of a solution

  Can be measured in mass per given volume of solution e.g. grams per dm^3 (g/dm^3)
• Calculating mass of solute in a given volume of a known concentration


  Use mass = conc x vol (think about the units!)
• Smaller volume or larger mass of solute


  Gives a higher concentration
• Larger volume or smaller mass of solute


  Gives a lower concentration
• Percentage yield

  Amount of product produced / Maximum amount of product possible x 100
• Reasons why calculated amount of product may not be obtained

  • Reaction may not go to completion because it is reversible
  • Some of the product may be lost when it is separated from the reaction mixture
  • Some of the reactants may react in ways different to the expected reaction
• Yield

  Amount of product obtained
• Calculating theoretical mass of a product

  1. Calculate mol. of reactant by using mol. = mass / molar mass

  2. Use balancing numbers to find mol. of product

  3. Calculate theoretical mass of a product by using mass = mol. x molar mass
• Atom economy

  A measure of the amount of starting materials that end up as useful products
• Atom economy is important for sustainable development and for economic reasons to use reactions with high atom economy
• Possible reasons why a particular reaction pathway is chosen/not chosen

  • Atom economy
  • Yield
  • Rate
  • Equilibrium position
  • Usefulness of by-products
• moles (mol) = volume (cm3) x concentration (mole dm3)
• Volume of gas (dm 3 ) at RTP = Moles x 24