TITRATIONS

• EQUIVALENCE POINT?

  when sufficient base has been added to neutralise the acid and vice versa (also known as stochiometric point)
• END POINT?

  when indicator just changes colour
• PROPERTIES OF A GOOD INDICATOR?

  • sharp colour change at end point
  • end point must be same as equivalence point
  • distinct colour change
  • soluble in water
• HOW DO INDICATORS WORK?

  • detect presence of H3O+ ions
  • act as weak acids
  • HIN (aq) ⇌ H+ (aq) + In- (aq)
  • HIN: colour A
  • IN-: colour B
• INDICATORS REACTION IN ACID?

  • H+ shift equilibrium
  • to reactants
  • produce colour A
• INDICATORS REACTION IN ALKALINE?

  • OH- react
  • remove H+
  • shift equilibrium to products
  • colour B
• CHANGES OF INDICATORS (ACID TO BASE)?

  METHYL ORANGE: red to yellow

  PHENOPHTHALEIN: colourless to pink

  BROMOTHYMOL BLUE: yellow to blue
• WHAT INDICATOR IS USED FOR STRONG ACID STRONG BASE REACTIONS?

  methyl orange, phenolphthalein, bromothymol blue

  -> phenolphthalein preferred due to most visible colour change
• WHAT INDICATOR IS USED FOR WEAK ACID WEAK BASE REACTIONS?

  none
• WHAT INDICATOR IS USED FOR STRONG ACID WEAK BASE REACTIONS?

  methyl orange
• WHAT INDICATOR IS USED FOR WEAK ACID STRONG BASE REACTIONS?

  phenolphthalein