3.10 - Alkalis are soluble bases
Distinguish bases from alkalis using solubility in water, and use examples to explain why every alkali is a base but not every base is an alkali.
Solubility adds a condition
A base neutralises an acid. An alkali is a base that is soluble in water. Its aqueous solution supplies hydroxide ions, OH⁻.
Sodium hydroxide and potassium hydroxide dissolve in water and form alkaline solutions, so both are alkalis. Copper(II) oxide is a base because it reacts with acids to form salt and water, but it is insoluble in water and is not an alkali.
| Substance | Base? | Soluble in water? | Classification |
|---|---|---|---|
| Sodium hydroxide | Yes | Yes | Alkali, and therefore a base |
| Potassium hydroxide | Yes | Yes | Alkali, and therefore a base |
| Copper(II) oxide | Yes | No | Base, not an alkali |
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