Write a chemical equation for Sr(OH)2(aq) showing how it is an acid or a base according to the Arrhenius definition.
The correct answer and explanation is :
Chemical Equation:
[
\text{Sr(OH)}_2(aq) \rightarrow \text{Sr}^{2+}(aq) + 2\text{OH}^-(aq)
]
Explanation (300 words):
Strontium hydroxide, Sr(OH)₂, is a classic example of a base under the Arrhenius definition. According to Svante Arrhenius, a base is a substance that increases the concentration of hydroxide ions (OH⁻) when dissolved in water. Conversely, an Arrhenius acid increases the concentration of hydrogen ions (H⁺), often represented as hydronium ions (H₃O⁺) in aqueous solution.
When Sr(OH)₂ dissolves in water, it completely dissociates into its ions: Sr²⁺ (a strontium ion) and 2 OH⁻ (hydroxide ions). The balanced chemical equation for this dissociation is:
[
\text{Sr(OH)}_2(aq) \rightarrow \text{Sr}^{2+}(aq) + 2\text{OH}^-(aq)
]
This reaction demonstrates that Sr(OH)₂ acts as an Arrhenius base because it directly releases hydroxide ions into the solution, increasing their concentration. These OH⁻ ions make the solution basic, which can be confirmed by using indicators like litmus paper (which turns blue in basic solutions) or pH measurements (which would show a pH above 7).
Strontium hydroxide is a strong base, meaning it dissociates completely in aqueous solution. This complete dissociation is typical of Group 2 metal hydroxides such as Ca(OH)₂ and Ba(OH)₂, although solubility can vary. Sr(OH)₂ is moderately soluble in water, but even this partial solubility is enough to produce a strongly basic solution due to the complete dissociation of the dissolved portion.
In summary, Sr(OH)₂ fits the Arrhenius definition of a base because it increases the hydroxide ion concentration in aqueous solution. This property allows it to neutralize acids in reactions and explains its behavior in various chemical processes involving bases.