Acid-Alkali Titration

• What would you observe when a alkaline solution with methyl orange is mixed with acid?


  Originally yellow with alkaline, turns orange then red as more acid is added.
• Phenolpthalein is pink in alkali what colour is it in acid?

  Colourless
• How do you set up a titration?

  Use a pipette to add a known volume of alkali to a conical flask, add a few drops of indicator and fill a burette with acid using a funnel.
• Why should you rinse the burette and pipette with the solutions they will contain before filling them? 


  To wash out any unwanted ions from the apparatus
• Once the apparatus has been prepared, how is a titration carried out?

  Open the tap of the burette to slowly add the solution to the conical flask, swirling to mix. Close the tap when the indicator shows neutralisation, record the volume and repeat.
• Why is an indicator used in titration?

  To show when the end point has been reached.
• Why is a white tile used in a titration?

  To make the colour change easier to see.
• Why should the conical flask be swirled during titration?

  To ensure the solution is completely mixed.
• What is the purpose of repeating a titration?

  To obtain concordant results, allowing a mean titre to be calculated and reduce the effect of a random error.
• Why is a trial titre carried out?

  To quickly check that the end-point can be reached using the concentrations and the volumes being used and to find the rough volume required to reach the end point.
• What are concordant results?

  Titres which are within 0.20 cm3 (or 0.10 cm3) of each other.
• How do calculate the mean titre?

  Add the 2 concordant results and divide by 2
• What is the end-point?

  When the indicator permanently changes colour.
• Why is a volumetric pipette used?

  Greater accuracy than an measuring cylinder
• If you know the volume of acid required to neutralise an acid, how can you calculate its concentration?

  Calculate the moles of alkali (vol x conc) and use the chemical equation to work out the ratio of acid and alkali, use that to find the moles of acid and divide it by the volume to find the concentration