2 - Neutralisation

• What is the method for this practical? (part 1)

  1. Use a pipette to measure 25cm3 of acid/alkali into a conical flask.
  2. Place the conical flask on a white tile.
  3. Fill a burette with acid/alkali (whichever opposes the first) using a funnel.
  4. Record the initial reading in the burette.
  5. Add 5 drops of indicator to the conical flask.
• What is the method for this practical? (part 2)

  6. Slowly open the burette tap while swirling the conical flask.

  7. Add the solution in the burette drop by drop near the endpoint.

  8. Close the burette when a colour change occurs.

  9. Record the final reading in the burette and calculate the titre.

  10. Repeat until you have concordant results.
• What is the method for this practical? (part 3)

  11. Present results in a table and calculate the mean titre, discarding any anomalies when calculating the mean.

  12. Calculate the number of moles in the flask’s solution.

  13. Apply the ratio from the balanced equation to find out the moles in the burette’s solution.

  14. Use the formula concentration = moles/volume to work out the concentration of burette solution.
• What does titre mean?

  The volume of a solution used for neutralisation.
• How far apart are concordant results?

  0.1cm3.
• To find the volume of sulfuric acid that will neutralize 25cm3 of sodium hydroxide solution:

  • Place 25cm3 of sodium hydroxide in a conical flask on a white tile
  • Clamp a burette above the flask and fill it with sulfuric acid
  • Add phenolphthalein to the flask
  • Slowly add sulfuric acid while swirling the flask
  • Close the burette tap when the mixture turns colorless
  • Record the final volume of sulfuric acid added
• Apparatus required for a titration:

  • Burette
  • Conical flask
  • Pipette and pipette filler
  • Funnel
  • Clamp and stand
  • White tile
• Reason for using a white tile in a titration experiment:

  • The white tile makes the color change easier to see under the reacting mixture
• Reason for using a volumetric pipette and pipette filler to measure 25cm3 in titrations:

  • Volumetric pipettes measure more accurately, crucial for titrations
• Purpose of repeating a titration:

  • To calculate a mean titre, reducing the effect of random error
• Colour of phenolphthalein in acid and alkali:

  • Acid: colorless
  • Alkali: pink
• Reason why the first trial in a titration is often called a 'rough' trial:

  • The first trial gives an approximate idea of the end point, aiding precision in subsequent titrations
• Safety precautions in a titration:

  • Wear eyewear and be aware of chemical dangers
  • Fill the burette below eye level
  • Clear any broken glassware immediately
• Reason for using burettes in titrations:

  • Burettes allow the solution to be added drop by drop in small quantities
• Other indicators for titrations and their color changes:

  • Methyl Orange: Red (acid) to yellow (alkali)
  • Litmus Blue: Red (acid) to blue (alkali)
• Calculating acid concentration given alkali concentration and volume:

  • Calculate moles of alkali
  • Use the chemical equation to find the ratio of acid and alkali reacting
  • Divide moles of acid by the volume used in neutralisation
• Converting acid concentration from mol/dm3 to g/dm3:

  • Multiply the concentration in mol/dm3 by the molar mass of the acid to get g/dm3