Acid-Base Titrations (Cambridge (CIE) O Level Chemistry): Revision Note

Acid-Base Titrations

• 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

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 thymolphthalein are very suitable

• Some of the most common indicators with their corresponding colours are shown below:

Common Acid-Base Indicators