Chapter 3

• What is Avogadro's constant?

  The number of particles per mole of a substance.

  =6.02 x 10^23
• How do you calculate the number of particles?

  (6.02 x 10^23) x (no: moles)
• What is the equation for moles?

  Moles (mol) = mass (g) / molar mass (g mol-1)
• What is the empirical formular?

  The simplest whole number ration of atoms of each element in a compound.
• What is the molecular formular?


  The actual number of atoms of each element in a compound.
• Define relative molecular mass?


  (Mr) compares the mass of a molecule to 1/12th of the mass of an atom of carbon - 12.
• Define relative formula mass?

  Compares the mass of a formula unit to 1/12th of the mass of an atom of carbon-12.
• Define a hydrated salt?

  An ionic solid containing water moleules.
• Define an anhydrous salt?

  An ionic solid containing no water molecules.
• What is the water of crystallisation?


  Water molecules in an ionic solid.
• How to calculate formula of hydrates salts?

  Heating a known amount of the substance until a "constant mass".
• What experimental errors occur in hydrated salts experiment?

  -not heating to constant mass - not all water evaporates (ratio would be too small)

  -further decompostion occurs
• How to cakculate percentage uncertainty?

  Percentage uncertainty = (uncertainty / measured value) x 100

  • uncertainty can by multiplied by the number of times the equpiment was used to reach the measured value
• How to reduce percentage uncertainty?

  Use a 3 d.p. balance

  Use a larger mass/volume of the substances
• What is the concentration equation?


  moles = conentration (mol dm-3) x volume (dm3)
• Define concentration?


  The amount of moles of substance dissolved in 1dm3 of a solution.
• Define standard solution?


  A solution of known concentration.
• Volume equation for gases at RTP?

  -temperature = 20C or 293K

  -Pressure = 101kPa

  Volume = molar gas volume (Vm) x moles
• What is Vm?


  Molar gas volume

  = 24dm3 mol-1

  =24000cm3 mol-1
• What is Avogadro's law?

  At the same temperature and pressure, equal volumes of different gases contain the same number of molecules.

  • 1 mole of any gas occupies the same volume at equal temperature and pressure
• What is the ideal gas equation?

  pV=nRT
• What defines as ideal gas?

  Particles are in random motion

  Collisions between particles are elastic

  No intermolecular forces

  Have a negligible size
• What is Boyle's law?

  Volume is inversely proportional to pressure
• What is Charle's law?

  Shows gas volume is affected by temperature
• Define Stoichiometry?


  The ratio of the amount, in moles, of each substance in a chemical reaction

  • shown in a balanced equation
• Define the limiting reagent?


  The reactant that is not in excess, which will used up first and stop the reaction

  • determining the maximum amount of the product that can be formed
• Define atom economy?


  A measure of how well the atoms have been utilised

  100% atom economy = no waster products / only 1 product is produced
• Define theoretical yield?


  Assuming all limiting reagent has reacted and been converted into products.

  This is hard because:

  • reaction may not have gone to completion
  • other (side) reactions may have also taken place
  • purification of the product may result in loss of some of the product
• Define actual yield?


  The yield of product obtained is usually lower than the theoretical yield
• What is the equation for percentage yield?

  Actual yield / theoretical yield x 100