Titrations

Titration is a widely used technique for determining the concentration of an unknown solution when the concentration of another solution is known. One of the most common types of titration is an acid-base titration.

In this technique, a carefully measured volume of the solution with an unknown concentration is placed into a conical flask, and a solution of known concentration is slowly added to it until the reaction is complete. The unknown solution is typically added from a burette

To determine when the reaction is complete, we often use an indicator, which changes colour to signal the endpoint of the reaction.

Apparatus

To perform an acid-base titration, you will need:

  • A pipette – To transfer a precise volume of the solution with an unknown concentration to a conical flask.
  • A burette – To accurately add small, measured volumes of an acid or alkali to the conical flask containing the other reactant.

Method

Let’s go through the steps involved in carrying out a titration:

1. Use the pipette to transfer a precise volume of alkali to a clean conical flask.

2. Add a few drops of indicator to the conical flask.

3. Fill the burette with the acid and record the initial volume reading.

4. Slowly add the acid from the burette to the alkali in the conical flask. After this, swirl the conical flask to ensure it is mixed thoroughly.

5. As you approach the endpoint of the reaction, add the acid drop by drop until you reach the endpoint.

  • The endpoint is when the indicator permanently changes colour

6. Record the final volume reading on the burette.

7. Repeat steps 1-6 until you get concordant titres.

  • Concordant titres are titre readings that are within 0.1 cm³ of each other. It is important to obtain concordant titres to ensure the accuracy of the results.
An illustration of the titration process, showing each step with labelled apparatus: the acid solution, pipette, and indicator.

Results

After completing the titration, it is important to record your results accurately. Here is an example of a table for recording results:

RunFinal reading (cm³)Initial reading (cm³)Titre (cm³)
Rough25.550.0025.55
126.550.5026.05 ✓
226.350.2026.15 ✓
Mean titre26.1

In this table:
run‘ refers to the trial number, and the ‘final reading’ and ‘initial reading’ refer to the volume of the titrant (the known solution) dispensed from the burette at the start and end of the titration, respectively. The ‘titre’ is the difference between the final and initial readings.

After recording your results in such a table, calculate the mean titre by adding up the titre values and dividing by the number of concordant titres.

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