3.2.6 REDOX Titration

• Name the piece of apparatus used for these stages of the method. [1 mark]

  • Taking the 25.0 cm3 portions
  • Graduated / volumetric PIPETTE
  • Adding the potassium manganate(VII) solution
  • Graduated / Volumetric BURETTE
• On Figure 1, draw the meniscus of the solution when the pipette is ready to transfer 25.0 cm3 of the sodium ethanedioate solution.

  • Meniscus curved with the bottom of the curve on the horizontal line

  
• Potassium manganate(VII) is oxidising and harmful.

  Sodium ethanedioate is toxic.

  Suggest safety precautions, other than eye protection, that should be taken when:

  • filling the burette with potassium manganate(VII) solution

  • (burette) fill below/at eye level

  • dissolving the solid sodium ethanedioate in water.

  • (solution) wear gloves
  • allow wash/rinse hands after any spillage
• Sodium ethanedioate is used to find the concentration of solutions of potassium manganate(VII) by titration.

  • In conical flask, sodium ethanedioate
  • In burette, potassium manganate

  STATE THE COLOUR CHANGE

  • colourless to PINK/PALE purple NOT just purple
  • NOT clear for colourless
• Figure 2 shows the burette containing potassium manganate(VII) solution.

  Give two practical steps needed before recording the initial burette reading.

  • remove funnel
  • ensure jet is filled / no (air) bubbles
  • ALLOW open tap to fill space below tap