Chemistry – Experimental techniques and chemical analysis - Acid-base titrations | e-Consult

Apparatus Required:

• 25.0 cm³ volumetric pipette
• Burette (50.0 cm³)
• Conical flask
• Distilled water
• Phenolphthalein indicator
• White tile
• Stirring rod

Procedure:

1. Carefully pipette 25.0 cm³ of the HCl solution into a clean conical flask. Rinse the pipette thoroughly with distilled water to ensure all the solution is transferred.
2. Add 2-3 drops of phenolphthalein indicator to the conical flask.
3. Fill the burette with distilled water, ensuring no air bubbles are present at the top. Record the initial reading of the burette to the nearest 0.05 cm³.
4. Slowly add the HCl from the burette to the conical flask while swirling the flask continuously. As the titration proceeds, the solution in the conical flask will gradually change from colorless to a faint pink colour around the endpoint.
5. Continue adding the HCl dropwise until a faint pink colour persists for at least 30 seconds when swirling the solution. This indicates the endpoint of the titration.
6. Record the final reading of the burette to the nearest 0.05 cm³.
7. Repeat the titration at least three times to obtain concordant results (results within 0.2 cm³).

Calculations:

The volume of HCl used in the titration is calculated by subtracting the initial burette reading from the final burette reading. The concentration of the HCl solution can then be calculated using the following equation:

Concentration of HCl (mol/dm³) = (Volume of HCl used in the titration (dm³) x Concentration of HCl (mol/dm³)) / Volume of solution in the conical flask (dm³)

Where the volume of solution in the conical flask is 0.025 dm³.