QUANTITATIVE CHEMISTRY

• Students should understand the use of the multipliers in equations in normal script before a formula and in subscript within a formula
• Relative formula mass (Mr)


  The sum of the relative atomic masses of the atoms in the numbers shown in the formula
• Students should be able to calculate the percentage by mass in a compound given the relative formula mass and the relative atomic masses
• Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas and its mass has not been taken into account
• Students should be able to explain any observed changes in mass in non-enclosed systems during a chemical reaction given the balanced symbol equation for the reaction and explain these changes in terms of the particle model
• Students should be able to represent the distribution of results and make estimations of uncertainty and use the range of a set of measurements about the mean as a measure of uncertainty
• Mole


  • The symbol for the unit mole is mol
  • 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
  • The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant, which has a value of 6.02 x 10^23 per mole
• Students should understand that the measurement of amounts in moles can apply to atoms, molecules, ions, electrons, formulae and equations
• Students should be able to use the relative formula mass of a substance to calculate the number of moles in a given mass of that substance and vice versa
• The masses of reactants and products can be calculated from balanced symbol equations
• Chemical equations can be interpreted in terms of moles
• Students should be able to calculate the masses of substances shown in a balanced symbol equation and calculate the masses of reactants and products from the balanced symbol equation and the mass of a given reactant or product
• Limiting reactant


  In a chemical reaction involving two reactants, the reactant that is completely used up, which limits the amount of products

  
• Students should be able to explain the effect of a limiting quantity of a reactant on the amount of products it is possible to obtain in terms of amounts in moles or masses in grams
• Concentration of solutions


  The concentration of a solution can be measured in mass per given volume of solution, eg grams per dm3 (g/dm3)
• Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product because the reaction may not go to completion, some of the product may be lost when it is separated from the reaction mixture, or some of the reactants may react in ways different to the expected reaction

  
• Volume of solution


  The mass of a solute and the volume of a solution is related to the concentration of the solution
• Yield


  The amount of a product obtained
• Percentage yield


  The yield compared with the maximum theoretical amount as a percentage
• Calculating percentage yield


  Mass of product actually made / Maximum theoretical mass of product x 100
• Calculating theoretical mass of a product


  From a given mass of reactant and the balanced equation for the reaction
• Atom economy


  A measure of the amount of starting materials that end up as useful products
• Calculating percentage atom economy

  Relative formula mass of desired product from equation / Sum of relative formula masses of all reactants from equation x 100
• It is important for sustainable development and for economic reasons to use reactions with high atom economy
• Concentration of a solution in mol/dm3

  Related to the mass of the solute and the volume of the solution
• The volume of one mole of any gas at room temperature and pressure (20oC and 1 atmosphere pressure) is 24 dm3
• Calculating volumes of gaseous reactants and products


  From a balanced equation and a given volume of a gaseous reactant or product