Acid-Alkali Titrations (Edexcel IGCSE Chemistry)

What is a titration?

• Titrations are a method of analysing the concentration of solutions
• Acid-base titrations are one of the most important kinds of titrations
• 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

How to carry out a titration

Performing a titration

Method

1. Use the pipette and pipette filler and place exactly 25 cm³ sodium hydroxide solution into the conical flask
2. Fill the burette with hydrochloric acid, place 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 (sharp colour change) and record the volume, placing your eye level with the meniscus
8. Now repeat the titration with a fresh batch of sodium hydroxide
9. 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
10. Record the volume to the nearest 0.05 cm³
11. Repeat until you achieve two concordant results (two results that are within 0.1 cm³ of each other) to increase accuracy

Results

Results table for a titration

Exam Hint Use a funnel to fill the burette but be sure to remove it before starting the practical as it can drip liquid into the burette, making the initial reading false.