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
• Using Equation 1


  1. Calculate the number of moles of CuSO4 in 35.0g of CuSO4

  2. Calculate the number of moles in 75.0mg of CaSO4.2H2O
• Avogadro's Constant


  6.022 x 10^23
• Calculating number of atoms/ions/molecules


  1. Calculate the number of atoms of tin in a 6.00 g sample of tin metal

  2. Calculate the number of chloride ions in a 25.0 cm3 of a solution of magnesium chloride of concentration 0.400 mol dm-3

  3. Calculate the number of molecules of ethanol in a 0.500 dm3 of ethanol (CH3CH2OH) liquid
• Calculating density


  Calculate the density of gold in a bar measuring 10 cm by 20 cm by 50 cm with 980 mol of pure gold
• Empirical formula


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


  The actual number of atoms of each element in the compound
• Determining empirical formula


  Calculate the empirical formula for a compound that contains 1.82g of K, 5.93g of I and 2.24g of O
• Heating in a crucible

  1. Weigh an empty clean dry crucible and lid

  2. Add 2g of hydrated calcium sulfate to the crucible and weigh again

  3. Heat strongly with a Bunsen for a couple of minutes

  4. Allow to cool

  5. Weigh the crucible and contents again

  6. Heat crucible again and reweigh until you reach a constant mass
• Determining water of crystallisation

  1. Calculate the value of the integer x in ZnSO4.xH2O

  2. Calculate the value of x in Na2SO4 . xH2O
• Concentration of solutions


  • Unit of concentration: mol dm-3 or M
  • Unit of volume: dm3
• Converting volumes


  1. cm3 to dm3: divide by 1000

  2. cm3 to m3: divide by 1,000,000

  3. dm3 to m3: divide by 1,000
• Calculating concentration of solution

  Calculate the concentration of solution made by dissolving 5.00 g of Na2CO3 in 250 cm3 water
• 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
• Moles


  mass/Mr
• Concentration


  moles/volume
• 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
• Solution


  Mixture formed when a solute dissolves in a solvent
• Molar concentration


  Calculated by dividing the amount in moles of the solute by the volume of the solution, measured in dm3
• Converting concentration mol dm-3 to g dm-3

  Multiply by Mr of the substance
• Mass concentration


  Concentration of a solution measured in terms of mass of solute per volume of solution, unit g dm-3
• Ions dissociating


  Soluble ionic solids dissolve in water and dissociate into separate ions
• Making a solution


  Weigh sample, transfer to beaker, add solvent, pour into volumetric flask, make up to mark
• Diluting a solution


  Pipette original solution into volumetric flask, make up to mark with solvent
• Calculating dilutions


  New diluted concentration = original concentration x original volume / new diluted volume
• Ideal gas equation


  PV = nRT
• Using a gas syringe

  Measure volume, temperature and pressure to calculate moles of gas
• Reacting volumes of gas

  Equal volumes of gases under same conditions contain equal moles, volumes can be calculated by simple ratio
• Equal volumes of any gases

  Measured under the same conditions of temperature and pressure, contain equal numbers of molecules (or atoms if the gas is monatomic)
• 1 mole of any gas

  At room pressure (1atm) and room temperature 25oC will have the volume of 24dm3
• Reacting volumes of gas

  Volumes of gases reacting in a balanced equation can be calculated by simple ratio