Chapter 12: Experimental Techniques and Chemical Analysis — Part 2

01 Purpose and Principles

Titrations are used to determine the exact concentration of an acid or alkali by finding the volume needed for neutralisation. They are also used to prepare pure soluble salts.

02 Apparatus and Method

The standard titration procedure involves:

1. Using a volumetric pipette to add a fixed volume of alkali (e.g., 25 cm³) into a conical flask.
2. Filling a burette with acid of unknown concentration using a funnel.
3. Recording the initial volume at eye level to the meniscus to the nearest 0.05 cm³.
4. Adding a few drops of a suitable indicator (e.g., phenolphthalein) and placing the flask on a white tile to make the colour change more visible.
5. Running the acid into the alkali while swirling until the end-point is reached.
6. Recording the final volume and calculating the titre (Final - Initial).
7. Repeating the process until two concordant results (within 0.1 cm³ of each other) are obtained to calculate a mean titre.

03 Identifying the End-Point

The end-point is identified by a sudden colour change of the indicator:

• Phenolphthalein: Pink in alkali ? Colourless in acid.
• Methyl Orange: Yellow in alkali ? Red in acid.