Acid-Base Titrations (Cambridge (CIE) IGCSE Chemistry)

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 perform titration calculations to determine the moles present in a given amount or the concentration / volume required to neutralise an acid or a base

• Titrations can also be used to prepare salts

Apparatus

• 25 cm³ volumetric pipette

• Pipette filler

• 50 cm³ burette

• 250 cm³ conical flask

• Small funnel

• 0.1 mol / dm³ sodium hydroxide solution

• Sulfuric acid of unknown concentration

• A suitable indicator

• Clamp stand, clamp & white tile

The steps in performing a titration

Method

1. Use the pipette and pipette filler and place exactly 25 cm³ sodium hydroxide solution into the conical flask

2. Using the funnel, fill the burette with hydrochloric acid placing an empty beaker underneath the tap. Run a small portion of acid through the burette to remove any air bubbles

3. Record the starting point on the burette to the nearest 0.05 cm³

4. Place the conical flask on a white tile so the tip of the burette is inside the flask

5. Add a few drops of a suitable indicator to the solution in the conical flask

6. Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm³ portions, while swirling the flask vigorously

7. Quickly close the tap when the end-point is reached 

   • The endpoint is when one drop causes a sharp colour change

8. Record the volume of hydrochloric acid added, in a suitable results table as shown below

   • Make sure your eye is level with the meniscus

9. Repeat the titration with a fresh batch of sodium hydroxide

10. 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

11. Record the volume to the nearest 0.05 cm³ 

12. 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 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