7.2.6 Carboxylic Acids as Acids

Ionisation of Carboxylic Acids:

• Partial Ionisation: When carboxylic acids dissolve in water, they partially ionise. This means that only a small fraction of the acid molecules release hydrogen ions (H⁺) into the solution, making the solution weakly acidic.
• Equilibrium Formation: Carboxylic acids establish an equilibrium between their ionised and non-ionised forms in water:

$$CH3COOH⇌H++CH3COO−$$

For example, ethanoic acid (CH₃COOH) is only about 5% ionised in water. This means that out of 100 ethanoic acid molecules, only about 5 will ionise to release H⁺ ions.

pH and Reaction Vigour:

• Weak Acidity: Because carboxylic acids only partially ionise, they create solutions with a pH of between 3 and 7, which is higher (less acidic) than the pH of strong acids like HCl.
• Slower Reactions: The weak ionisation also means that the reactions of carboxylic acids are often slower and less vigorous than those of strong acids. Some reactions might be barely noticeable at room temperature.