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Difficulty: MediumAluminium: Extraction, Amphoteric Properties, Alloys, and Compounds

When aluminium metal is dissolved in a concentrated aqueous solution of sodium hydroxide, a gas is evolved and a soluble complex ion is formed in the solution. What are the chemical formulas of the gas evolved and the complex ion formed, respectively?

  1. H2H_2 and [Al(OH)4]−[Al(OH)_4]^-Answer
  2. B
    O2O_2 and [Al(OH)4]−[Al(OH)_4]^-
  3. C
    H2H_2 and Al3+Al^{3+}
  4. D
    NH3NH_3 and [Al(OH)4]−[Al(OH)_4]^-

Answer

The gas evolved is hydrogen gas (H2H_2) and the complex ion formed is the tetrahydroxoaluminate(III) ion ([Al(OH)4]−[Al(OH)_4]^-).
Aluminium metal exhibits amphoteric behavior, dissolving in strong alkaline solutions such as aqueous sodium hydroxide. The reaction oxidizes aluminium metal to form the soluble aluminate complex ion, [Al(OH)4]−[Al(OH)_4]^-, while reducing hydrogen species to yield hydrogen gas, H2H_2.

Step-by-Step Solution

1
Identify the amphoteric property of aluminium metal in basic solutions.
Aluminium reacts with both acids and strong bases (alkalis) such as sodium hydroxide.
Aluminium forms protective oxide layers and has amphoteric chemical behavior.
2
Write the balanced ionic reaction between aluminium metal, hydroxide ions, and water.
2Al(s)+2OH−(aq)+6H2O(l)→2[Al(OH)4]−(aq)+3H2(g)2Al(s) + 2OH^-(aq) + 6H_2O(l) \rightarrow 2[Al(OH)_4]^-(aq) + 3H_2(g)
Aluminium is oxidized to the soluble tetrahydroxoaluminate(III) complex ion, while water/hydrogen species are reduced to hydrogen gas.
3
Match the products to the question requirements.
Gas evolved: H2H_2; Soluble complex ion: [Al(OH)4]−[Al(OH)_4]^-
The reaction produces hydrogen gas and tetrahydroxoaluminate(III).

Key Concept

Amphoteric Nature of Aluminium and Reaction with Strong Alkalis
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Topics

Aluminium: Extraction, Amphoteric Properties, Alloys, and Compounds

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