amount of substance

• relative atomic mass equation

  $sum\ of\left(mass\times abundance\ of\ each\ isotope\right)\div total\ abundance$
• the mole

  the amount of substance that contains as many particles as there are in exactly 12g of carbon-12
• the ideal gas equation

  pV=nRT
• empirical formula

  the simplest whole number ratio of atoms of each element present in a molecule
• molecular formula

  the actual number of atoms of each element present in a molecule
• how to make a standard solution

  • record the mass of a weighing boat and solid
  • tip the solid into a beaker and record the mass of the weighing boat
  • determine the mass of solid used by calculating the difference
  • dissolve the solid in deionised water
  • using a funnel, transfer into a volumetric flask, include washings
  • make up to the graduated line by carefully adding deonised water making sure the meniscus sits on the line
  • stopper the flask and invert to mix the contents thoroughly
• to find the concentration of a solution of a base

  • fill a burette with a standard solution of the acid
  • pipette a known volume of base into conical flask
  • add a few drops of indicator to the base in the flask
  • add the solution of the acid from the burette until the indicator just changes colour. this is known as the end point
  • record the volume of acid added: record your burette readings to the nearest 0.05cm3
  • perform a rough titration and then sufficient accurate ones until the titres are concordant
  • calculate the mean titre from the concordant titres- to 2d.p.
• percentage error

  $\frac{uncertainty}{value}\times100$
• to calculate the number of moles of water of crystallisation

  • need to know the masses of the hydrated and anhydrous salts
  • mass of water= mass hydrated salt- mass anhydrous salt
  • work out the number of moles of anhydrous salt and of water
  • find the simplest whole number ratio
• percentage yield

  $\frac{actual\ yield}{theoretical\ yield}\times100$
• reasons for a low percentage yield

  • incomplete reaction/ reversible reaction
  • side reactions may occur
  • loss of product during transfer or purification steps
  • impurities in the reactants
• atom economy

  $\frac{Mr\ desired}{Mr\ total}\times100$