Core Practical: Acid-Alkali 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:
- Use the pipette and pipette filler and place exactly 25 cm3 sodium hydroxide solution into the conical flask
- Place the conical flask on a white tile so the tip of the burette is inside the flask
- Add a few drops of a suitable indicator to the solution in the conical flask
- Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm3 portions, while swirling the flask vigorously
- Quickly close the tap when the end-point is reached (sharp colour change) and record the volume, placing your eye level with the meniscus
- Now repeat the titration with a fresh batch of sodium hydroxide
- 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
- Record the volume to the nearest 0.05 cm3
- Repeat until you achieve two concordant results (two results that are within 0.1 cm3 of each other) to increase accuracy
Record your results in a suitable table, e.g:
Exam Tip
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.
Hazards, risks and precautions
Hazard symbol to show substances that are harmful to health
- Dilute hydrochloric acid is not classified as hazardous at the concentrations typically used in this practical, however it may still cause harm to the eyes or the skin
- Sodium hydroxide may be considered to be harmful to health, depending on the concentration used as it is irritating to the eyes and skin
- For both sodium hydroxide and hydrochloric acid, avoid contact with the skin and use safety goggles
