6.3.1 Strength of Acids and Alkalis
Strong Acids and Weak Acids
- Acids are chemical substances that ionize/dissociate in the presence of water to produce hydrogen ions (or hydroxonium ions).
- Acids can be classified into 2 categories:
- Strong acids
- Weak acids
- The strength of an acid depends on the degree of ionization/dissociation of the acid.
Strong Acids
Strong acids are acids that ionise completely to form hydrogen ions in water.
Examples:
Sulphuric acid
Hydrochloric acid
Nitric acid
Weak Acids
Weak acids are acids that partly ionise to form hydrogen ions in water.
Examples:
Ethanoic acid
Phosphoric acid
Citric acid
Strength of Alkali
- Similar to the strength of acids, the strength of an alkali is defined by its ability to ionise and release hydroxide ions (OH–) in the solution.
- In a solution of strong alkali, all the alkali molecules are ionised in the water to produce hydroxide ions.
- In a solution of weak alkali, only a small portion of the molecules are ionised to release hydroxide ions.
- The table below shows some example of strong/weak alkalis.
Alkali | |
Strong | Weak |
| NaOH KOH LiOH | NH3 |