T5

• Mole


  A unit of measurement for substances that always contains the same number of particles
• Avogadro Constant (L)


  Allows the number of particles present in a sample of a substance with known mass to be found
• Molar mass


  The mass in grams per mole of a substance, with units g mol-1

  
• Relative atomic mass (Ar)


  The mean mass of an atom of an element, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope

  
• Relative molecular mass (Mr)


  The mean mass of a molecule of a compound, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope

  
• Relative formula mass


  For ionic compounds, the relative molecular mass

  
• Empirical formula


  The simplest whole number ratio of atoms of each element in a compound, found using molar ratios

  
• Molecular formula


  The actual number of each atom in the molecule, determined using the Mr of the empirical formula and the true Mr of the molecule

  
• The Ideal Gas Equation

  1. Pressure is proportional to Temperature

  2. Volume is proportional to Temperature

  3. Pressure and Volume are inversely proportional
• Balanced chemical equation


  Has the same number and type of each atom present on both sides of the equation
• State symbols


  • (s) - solid
  • (l) - liquid
  • (g) - gas
  • (aq) - aqueous (dissolved in water)
• Ionic equation


  Shows just the reacting particles that undergo a change during the reaction and not the spectator species
• Percentage yield


  Indicates how much of the maximum amount of product was obtained during an experiment
• Atom economy


  A measure of efficiency, the proportion of reactant atoms which are converted into the desired product

  
• Volumetric Solution - Simple Method

  1. Weigh sample bottle

  2. Transfer solid to beaker and reweigh

  3. Record mass difference

  4. Dissolve solid in water

  5. Transfer to volumetric flask and make up to mark

  6. Shake flask
• Titration - Simple Method

  1. Fill burette with standard solution

  2. Transfer 25cm3 of unknown solution to conical flask

  3. Add indicator

  4. Record initial burette reading

  5. Titrate until indicator colour change

  6. Record final burette reading

  7. Repeat for concordant results
• Percentage uncertainty


  Can be calculated if the uncertainty of the instrument is known

  
• The best way to reduce uncertainties in a titration is to increase the titre volume needed for the reaction
• It is important to carry out a risk assessment before undertaking any practical work