Amount of substance

• Define mr 


  Mr= average mass of one molecule / 1/12 the mass of one atom of 12 cl
• Empirical formula 


  The simplest whole number ratio of each element in an compound
• define molecular formula 


  the actual number of each element in a compound
• How to calculate empirical formula / molecular formula 


  1 divide percentage by ar of each element

  2 divide each ratio by smallest ratio

  3 for molecular calculate mr of empirical formula

  4 find scaling ratio of molecular formula to empirical formula by dividing molecular formula by mr
• Conversation for mass 


  Ug - mg - g-kg- tonne - = x10-3

  tonne -kg-g-mg-ug - =x10 3
• Density formula 


  Density =mass/volume
• Percentage yield formula 


  Percentage yield = actual mass / theoretical mass x100
• How to calculate percentage yield

  1 calculate moles of limiting regant

  2 use molar ratios to calculate moles of maximum mass

  3 convert into mass

  4 substitute into equation
• Atom economy formulas 


  Atom economy = mass of desired product / mass of reactants x100

  atom economy = mol mass of desired products /mol x mass of reactants x 100
• Concentration formula 


  N=cxv
• ideal gas equation 


  PV =NRT
• Combined gas law 


  P1 v1/T1 = p2 v2/ t2
• Weigh by difference

  1. Weigh mass of bottle + lid + content
  2. empty content of bottle into a beaker
  3. weigh empty bottle and lid
  4. add approximately 100cm3 of distilled water and stir with glass rod to dissolve solvent
  5. pour solution into a volumetric flask and add washing
  6. top up to the 250cm3 mark
  7. add lid and invert 3 times
• Titrations


  A laboratory method used to determine the concentration of a solution
• Titration procedure

  1. Rinse burette and pipette

  2. Use conical flask

  3. Fill burette using a funnel

  4. Remove funnel during titration

  5. Add indicator

  6. Swirl solution

  7. Rinse near endpoint with distilled water
• Rinse burette and pipette with reagent used in them to remove contaminants
• Use conical flask instead of a beaker to reduce loss of solution when adding or swirling
• Fill burette using a funnel ensuring tap is full; if not, increase volume for accuracy
• Funnel is removed during titration; solution may drop from funnel, decreasing the volume
• Only 2-3 drops of indicator are added as they are weak acids and can change the titre
• If base is in burette

  Titre volume would increase (moles of base in flask decrease due to excessive indicator added)
• If acid is in burette

  Titre volume would decrease (moles of base in flask decrease due to excessive indicator added)
• Solution is swirled while adding solutions from flask to burette to mix reactants and ensure immediate reaction
• Near endpoint, sides of conical flask are rinsed with distilled water to ensure all reactants are in the flask to react
• Endpoint is not affected; it does not change moles of acid and base, and water is not a reactant