Quantitative Chemistry

• Relative formula mass

  The mass of a compound calculated from the relative atomic masses of its constituent elements
• Calculating relative formula mass


  1. Look at the relative atomic masses of each element in the compound

  2. Multiply each element's relative atomic mass by the number of that element in the compound

  3. Add up the masses of all the elements
• Mole


  A unit of measurement equal to 6.022 x 10^23 atoms or molecules
• One mole of a substance is equal to the substance's relative atomic/formula mass in grams
• Calculating moles

  Moles = Mass / Relative formula mass
• A balanced chemical equation shows the mole ratios of reactants and products
• Mass is conserved in a chemical reaction
• Calculating theoretical yield

  1. Balance the chemical equation

  2. Calculate moles of limiting reactant

  3. Use mole ratios to calculate moles of product

  4. Convert moles of product to mass using relative formula mass
• Percentage yield

  Actual yield / Theoretical yield x 100
• Percentage yields are important in chemistry as reactions rarely go to completion
• It's very unlikely that you would actually ever make 2.2 grams of iron from the reaction of iron oxides with carbon, you'll usually make less because you can never carry out a reaction to its fullest and sometimes you get a bit of transfer loss, it usually results in a value of around 1.9 grams of iron
• Percentage yield


  How much you make compared to the theoretical, calculated by dividing the actual yield by the theoretical yield
• Percentage yields are massively important for chemists because they need to know how successful their reactions are and whether they're losing a lot of their reaction reactants
• Atom economy


  How much of a percent of the starting materials ends up as useful products and not wasted
• Reactions with high atom economy are better for industry
• Concentration


  Can be calculated by mass/volume or moles/volume
• Dilute solution

  Has little solid dissolved in the liquid
• Concentrated solution


  Has lots of solid dissolved in the liquid
• To make a solution more dilute, add more liquid. To make it more concentrated, add more solid
• Concentration can be represented in units of g/cm3, g/dm3, mol/cm3, mol/dm3
• Titration


  Used to calculate the unknown concentration of an acid or alkali
• Titration procedure

  1. Unknown acid in conical flask

  2. Alkali in burette

  3. Indicator used to show neutralisation point
• Moles of gas


  Volume of gas / 24 dm3 or 24,000 cm3