Acid-Base Titrations (CIE IGCSE Chemistry)

• Titrations are a method of analysing the concentration of solutions
• They can determine exactly how much alkali is needed to neutralise a quantity of acid – and vice versa
• You may be asked to calculate the moles present in a given amount, the concentration or volume required to neutralise an acid or a base
• Titrations can also be used to prepare salts

Describing how to carry out a titration

• The typical materials needed are:
  • 25 cm³ volumetric pipette
  • Pipette filler
  • 50 cm³ burette
  • 250 cm³ conical flask
  • Small funnel
  • 0.1 mol/dm³ sodium hydroxide solution
  • Sulfuric acid – concentration unknown
  • A suitable indicator
  • Clamp stand, clamp & white tile

The steps in performing a titration

Describing the method:

1. Use the pipette and pipette filler and place exactly 25 cm³ sodium hydroxide solution into the conical flask
2. Place the conical flask on a white tile so the tip of the burette is inside the flask
3. Add a few drops of a suitable indicator to the solution in the conical flask
4. Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm³ portions, while swirling the flask vigorously
5. Quickly close the tap when the end-point is reached (sharp colour change) and record the volume, placing your eye level with the meniscus
6. Now repeat the titration with a fresh batch of sodium hydroxide
7. As the rough end-point volume is approached, add the solution from the burette one drop at a time until the indicator just changes colour
8. Record the volume to the nearest 0.05 cm³
9. Repeat until you achieve two concordant results (two results that are within 0.1 cm³ of each other) to increase accuracy

Indicators

• Indicators are used to show the endpoint in a titration
• Wide range indicators such as litmus are not suitable for titration as they do not give a sharp enough colour change at the endpoint
• However, methyl orange and phenolphthalein are very suitable
• Some of the most common indicators with their corresponding colours are shown below:

Common Acid-Base Indicators