Analytical Methods - Titrations (SQA National 5 Chemistry): Revision Note

Titrations

• Titration is an accurate experimental method used to determine the exact volume of a solution needed to react completely with another solution

  • They can also be used to prepare soluble salts

• This data can then be used in calculations to find an unknown concentration

Key terminology

• Standard solution

  • A standard solution is one where the concentration is known precisely

  • In a titration, this is the solution you use to find the concentration of the "unknown" solution

• End-point

  • The end-point is the point at which the reaction is just complete (e.g., the acid has perfectly neutralised the alkali)

  • It is identified by a sharp, permanent colour change in the indicator.

• Titre

  • The titre is the volume of solution added from the burette to reach the end-point

Apparatus used in a titration

Method

1. Use the pipette and pipette filler and place exactly 25 cm³ of alkali into the conical flask

2. Fill the burette with acid, place an empty beaker underneath the tap and 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 0.2 cm³ of each other) to increase accuracy

Practical 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

Example results 

• Calculate mean titre using concordant results, 14.90 cm³ and 15.00 cm³

• Average titre = (14.90 + 15.00) / 2 = 14.95 cm³