A strong base is primarily characterized by its complete ionization in water.
Understanding Strong Bases
According to the reference, "The main characteristic of a strong acid or base is that it completely ionizes in water." This is the fundamental property that defines a strong base. When a strong base dissolves in water, it dissociates entirely into its constituent ions, including hydroxide ions ($\text{OH}^-$). This high concentration of hydroxide ions is what gives a strong base its potent alkaline properties.
The Ionization Process
Unlike weak bases, which only partially ionize, a strong base undergoes 100% dissociation in aqueous solution. For example, if you dissolve a strong base like sodium hydroxide ($\text{NaOH}$) in water, every $\text{NaOH}$ molecule will break apart into a sodium ion ($\text{Na}^+$) and a hydroxide ion ($\text{OH}^-$).
$\text{NaOH(s)} \xrightarrow{\text{H}_2\text{O}} \text{Na}^+\text{(aq)} + \text{OH}^-\text{(aq)}$
This complete separation leads to a very high concentration of $\text{OH}^-$ ions, making the solution highly basic and reactive.
Key Characteristics Summarized
Here's a simple breakdown of what defines a strong base:
- Complete Ionization: Dissociates 100% in water.
- High $\text{OH}^-$ Concentration: Produces the maximum possible concentration of hydroxide ions for its given concentration.
- High pH: Results in solutions with very high pH values (typically above 13 for common concentrations).
- Strong Electrolyte: Due to complete ionization, strong base solutions conduct electricity very well.
Common Examples of Strong Bases
Most strong bases are hydroxides of alkali metals and some alkaline earth metals.
- Alkali Metal Hydroxides:
- Lithium Hydroxide ($\text{LiOH}$)
- Sodium Hydroxide ($\text{NaOH}$)
- Potassium Hydroxide ($\text{KOH}$)
- Rubidium Hydroxide ($\text{RbOH}$)
- Cesium Hydroxide ($\text{CsOH}$)
- Heavy Alkaline Earth Metal Hydroxides:
- Calcium Hydroxide ($\text{Ca(OH)}_2$) - Note: Solubility is lower than alkali metal hydroxides, but what dissolves ionizes completely.
- Strontium Hydroxide ($\text{Sr(OH)}_2$)
- Barium Hydroxide ($\text{Ba(OH)}_2$)
Understanding that a strong base completely ionizes is crucial for predicting its behavior in chemical reactions, such as neutralization reactions with acids.
