Problem 116
Question
The dissolution of \(\mathrm{Al}(\mathrm{OH})_{3}\) by a solution of \(\mathrm{NaOH}\) results in the formation of (a) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}(\mathrm{OH})_{3}\right]\) (b) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}(\mathrm{OH})\right]^{2+}\) (c) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}(\mathrm{OH})_{4}\right]^{-}\) (d) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3}(\mathrm{OH})_{3}\right]\)
Step-by-Step Solution
Verified Answer
The correct answer is option (c) \( \left[\mathrm{Al}\left(\mathrm{H}_2\mathrm{O}\right)_2(\mathrm{OH})_4\right]^- \).
1Step 1: Understand the Reaction Context
The problem involves the dissolution of aluminum hydroxide, \( \mathrm{Al(OH)}_3 \), in a sodium hydroxide \( \mathrm{NaOH} \) solution. Aluminum hydroxide is amphoteric, meaning it can dissolve in both acids and bases. In strong base solutions, aluminum hydroxide dissolves to form soluble aluminate ions.
2Step 2: Identify the Reactants and Products
When \( \mathrm{Al(OH)}_3 \) dissolves in an excess of \( \mathrm{NaOH} \), it reacts to form the aluminate ion \( [\mathrm{Al(OH)}_4]^- \). Since sodium ions are spectator ions, they do not form part of the product. The product of this reaction is \( \left[\mathrm{Al(OH)}_4\right]^- \).
3Step 3: Match the Product with Given Options
Based on the reaction, \( [\mathrm{Al(OH)}_4]^- \) is formed. Comparing with the given options, it corresponds to (c) \( \left[\mathrm{Al}\left(\mathrm{H}_2\mathrm{O}\right)_2(\mathrm{OH})_4\right]^- \). This representation uses the hydrate form, indicating the number of water molecules typically found in the coordination sphere of the metal ion.
4Step 4: Confirm the Coordination Chemistry
The presence of \( \mathrm{H}_2\mathrm{O} \) molecules in the complex is common in such structures, where water molecules coordinate with the aluminum ion. Thus, option (c) properly represents the complex formed from the dissolution of \( \mathrm{Al(OH)}_3 \) in \( \mathrm{NaOH} \).
Key Concepts
Amphoteric BehaviorCoordination ChemistrySodium Hydroxide Reaction
Amphoteric Behavior
Amphoteric substances have the unique ability to behave both as acids and bases. This property allows them to react with both strong acids and strong bases, leading to different reaction products.
Aluminum hydroxide \(\mathrm{Al(OH)}_3\) is an example of an amphoteric compound.
This means that in acidic environments, it donates hydroxide ions, while in basic environments, it accepts protons.
This dual ability makes it versatile in reactions.
When \(\mathrm{Al(OH)}_3\) is placed in a basic solution like sodium hydroxide \(\mathrm{NaOH}\), it dissolves by interacting with the \(\mathrm{OH}^-\) ions in the solution, forming the aluminate ion \(\left[\mathrm{Al(OH)}_4\right]^-\).
The reaction showcases the amphoteric nature of \(\mathrm{Al(OH)}_3\) and explains its solubility in basic solutions.
Understanding amphoteric behavior is crucial as it helps predict how a substance will behave in different chemical environments.
Aluminum hydroxide \(\mathrm{Al(OH)}_3\) is an example of an amphoteric compound.
This means that in acidic environments, it donates hydroxide ions, while in basic environments, it accepts protons.
This dual ability makes it versatile in reactions.
When \(\mathrm{Al(OH)}_3\) is placed in a basic solution like sodium hydroxide \(\mathrm{NaOH}\), it dissolves by interacting with the \(\mathrm{OH}^-\) ions in the solution, forming the aluminate ion \(\left[\mathrm{Al(OH)}_4\right]^-\).
The reaction showcases the amphoteric nature of \(\mathrm{Al(OH)}_3\) and explains its solubility in basic solutions.
Understanding amphoteric behavior is crucial as it helps predict how a substance will behave in different chemical environments.
Coordination Chemistry
Coordination chemistry explores how metal atoms or ions are surrounded by molecules or ions, known as ligands, which are bonded to the central metal ion.
These complexes significantly impact many chemical reactions and properties.
For instance, in the aluminate ion \(\left[\mathrm{Al(OH)}_4\right]^-\), aluminum is the central metal ion.
Ligands like hydroxide and water molecules coordinate around the metal.
These interactions form stable structures, known as coordination complexes.
The metal-ligand interactions involve sharing of electron pairs, which stabilizes the entire structure.
In this exercise, the aluminum ion in the aluminate complex is surrounded by four hydroxide ions, highlighting its typical coordination behavior.
Coordination chemistry helps explain how such complexes are formed and predict the structures and properties of various compounds.
These complexes significantly impact many chemical reactions and properties.
For instance, in the aluminate ion \(\left[\mathrm{Al(OH)}_4\right]^-\), aluminum is the central metal ion.
Ligands like hydroxide and water molecules coordinate around the metal.
These interactions form stable structures, known as coordination complexes.
The metal-ligand interactions involve sharing of electron pairs, which stabilizes the entire structure.
In this exercise, the aluminum ion in the aluminate complex is surrounded by four hydroxide ions, highlighting its typical coordination behavior.
Coordination chemistry helps explain how such complexes are formed and predict the structures and properties of various compounds.
Sodium Hydroxide Reaction
The reaction of aluminum hydroxide \(\mathrm{Al(OH)}_3\) with sodium hydroxide \(\mathrm{NaOH}\) is an example of how amphoteric substances can interact with bases.
In this case, \(\mathrm{NaOH}\) acts as a strong base, providing \(\mathrm{OH}^-\) ions that facilitate the dissolution of \(\mathrm{Al(OH)}_3\).
The process leads to the formation of the aluminate ion \(\left[\mathrm{Al(OH)}_4\right]^-\).
This reaction occurs because the sodium ions are spectator ions—they do not participate directly in the formation of the reaction's main product.
This specific reaction highlights sodium hydroxide’s ability to transform the structure of amphoteric compounds.
It is an example of how a base can extend the solubility of a compound by creating stable, soluble ionic complexes.
Studying such reactions helps in understanding the broader impacts of chemical behavior in various solutions.
In this case, \(\mathrm{NaOH}\) acts as a strong base, providing \(\mathrm{OH}^-\) ions that facilitate the dissolution of \(\mathrm{Al(OH)}_3\).
The process leads to the formation of the aluminate ion \(\left[\mathrm{Al(OH)}_4\right]^-\).
This reaction occurs because the sodium ions are spectator ions—they do not participate directly in the formation of the reaction's main product.
This specific reaction highlights sodium hydroxide’s ability to transform the structure of amphoteric compounds.
It is an example of how a base can extend the solubility of a compound by creating stable, soluble ionic complexes.
Studying such reactions helps in understanding the broader impacts of chemical behavior in various solutions.
Other exercises in this chapter
Problem 113
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