Amount of substance

• Mole


  The amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12
• Avogadro's Number


  There are 6.022 x 10^23 atoms in 12 grams of carbon-12
• One mole of any specified entity contains 6.022 x 10^23 of that entity
• Equations used for most calculations at A-level

  • For pure solids, liquids and gases
  • For gases: PV = nRT
  • For solutions
• Relative atomic mass


  The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
• Relative molecular mass


  The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
• Molar mass (Mr) for a compound can be calculated by adding up the mass numbers (from the periodic table) of each element in the compound
• Give your answers to the same number of significant figures as the number of significant figures for the data you given in a question
• Calculating moles from mass

  moles = mass / Mr
• Converting units


  • 1000 mg = 1g
  • 1000 g = 1 kg
  • 1000 kg = 1 tonne
• Avogadro's constant can be used for atoms, molecules and ions
• Calculating number of particles from moles

  No of particles = moles of substance (in mol) X Avogadro's constant
• Density is usually given in g cm-3
• Calculating mass from density and volume

  mass = density x volume
• Calculating molecular formula from empirical formula


  Work out how many times the mass of the empirical formula fits into the Mr
• Empirical formula


  The simplest ratio of atoms of each element in the compound
• Calculating empirical formula


  Step 1: Divide each mass (or % mass) by the atomic mass of the element

  Step 2: For each of the answers from step 1 divide by the smallest one of those numbers

  Step 3: Sometimes the numbers calculated in step 2 will need to be multiplied up to give whole numbers
• Hydrated salt


  Contains water of crystallisation
• Heating hydrated salts in a crucible


  Weigh empty crucible, add hydrated salt, heat, allow to cool, reweigh until constant mass
• Heating in a crucible can be used for measuring mass loss in various thermal decomposition reactions and also for mass gain when reacting magnesium in oxygen
• Calculating water of crystallisation in hydrated salts

  Calculate moles of anhydrous salt and moles of water, then find ratio to determine value of x in formula
• Concentration of solutions


  Measured in mol dm-3 or M
• Calculating concentration of a solution

  concentration = moles / volume
• A cm3 is equivalent to a cube 1cm x 1cm x 1cm, a dm3 is equivalent to a cube 10cm x 10cm x 10cm, and a m3 is equivalent to a cube 100cm x 100cm x 100cm
• 1 dm3 = 1000 cm3 or 1000 mL, 1 m3 = 1000 dm3 or 1000 L
• To convert cm3 into dm3, divide by 1000. To convert m3 into dm3, multiply by 1000
• Solution


  A mixture formed when a solute dissolves in a solvent
• Ration


  mol dm-3 or M
• Unit of volume


  dm3
• Converting volumes


  1. cm3 to dm3 ÷ 1000

  2. cm3 to m3 ÷ 1000 000

  3. dm3 to m3 ÷ 1000
• cm3


  Equivalent to a cube 1cm x 1cm x 1cm
• dm3


  Equivalent to a cube 10cm x 10cm x 10cm = 1000 cm3
• m3


  Equivalent to a cube 100cm x 100cm x 100cm = 1000000 cm3
• 1 cm3 = 1 mL
• 1 dm3 = 1 litre
• 1 dm3 = 1000 cm3 or 1000 mL
• Converting cm3 to dm3

  Divide by 1000
• Converting m3 to dm3

  Multiply by 1000
• Molar concentration


  Calculated by dividing the amount in moles of the solute by the volume of the solution, measured in dm3. Unit is mol dm-3 or M
• Mass concentration


  Concentration of a solution measured in terms of mass of solute per volume of solution. Unit is g dm-3