AQA GCSE FOUNDATION Chemistry: Strong and Weak Acids

Strong and Weak Acids: Understanding Ionization

Acids are substances that release hydrogen ions (H+) when dissolved in water. This process is called ionization. The strength of an acid depends on how readily it ionizes in solution.

Strong Acids: Complete Ionization

Strong acids ionize completely in water, meaning every molecule of the acid donates its hydrogen ion. This results in a high concentration of H+ ions in the solution.

Example:

• Hydrochloric acid (HCl) is a strong acid. When dissolved in water, it ionizes completely to form hydrogen ions (H+) and chloride ions (Cl-):

HCl(aq) ? H+(aq) + Cl-(aq) 

Weak Acids: Partial Ionization

Weak acids only partially ionize in water, meaning only a small proportion of the acid molecules donate their hydrogen ions. This results in a lower concentration of H+ ions in the solution compared to strong acids.

Example:

• Ethanoic acid (CH3COOH) is a weak acid. When dissolved in water, it only partially ionizes to form hydrogen ions (H+) and ethanoate ions (CH3COO-):

CH3COOH(aq) ? H+(aq) + CH3COO-(aq) 

The double arrow (?) indicates that the reaction is reversible. This means that some of the ethanoate ions can recombine with hydrogen ions to form ethanoic acid again.

Key Differences:

Summary:

• Strong acids completely ionize in solution, resulting in a high concentration of H+ ions.
• Weak acids partially ionize in solution, resulting in a lower concentration of H+ ions.
• The strength of an acid is determined by its ability to donate hydrogen ions.