Dissociation equilibrium with Cobra SMARTsense

Principle

Carboxylic acids are potential electrolytes which exist in a weakly dissociated condition in aqueous solutions. The location of the dissociation equilibrium is quantitatively described by the Ka or pKa value which can be determined with potentiometric measurements.

Benefits

• Simplified implementation: all pre-settings already prepared
• Drop counter optimizes the experimental procedure

Tasks

1. Measure the alteration of the pH value during a titration of approximately 0.1 molar aqueous solutions of formic acid, acetic acid, monochloroacetic acid, propionic acid, butyric acid and lactic acid with a 0.1 molar sodium hydroxide solution at constant temperature using Cobra SMARTsense-system.
2. From the neutralisation curves read the pKa values of the acids and compare them.

Learning objectives

• True and potential electrolytes
• Strong and weak acids
• Law of mass action
• Henderson-Hasselbalch equation
• Dissociation constant and pKa value
• Substituent effects
• Potentiometry

Necessary accessories

• Precision balance 620g/0.001g

Software included. Computer not provided.