Amphoteric Nature of aluminium , zinc, and lead - metals, oxides, and hydroxides

Amphoteric Nature

Amphoteric substances react with both acids and bases, acting as acids with bases (accepting OH⁻) and as bases with acids (donating OH⁻ or accepting H⁺). Aluminium, zinc, and lead (to a lesser extent) exhibit this property in their metals, oxides, and hydroxides.

Summary

• Aluminium: Metal, oxide, and hydroxide react readily with NaOH (forming aluminates) and HCl (forming chlorides), showing strong amphoterism.
• Zinc: Similar to aluminium, forms zincates with NaOH and chlorides with HCl, though metal requires concentrated alkali.
• Lead: Oxide and hydroxide are amphoteric, forming plumbites with NaOH and chlorides with HCl; metal is less reactive with NaOH.

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DETAILS

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1. Aluminium (Al)

Aluminium Metal

• With NaOH: Reacts to form sodium aluminate and hydrogen gas: $$2Al(s) + 2NaOH(aq) + 6H₂O(l) \rightarrow 2NaAl(OH)₄(aq) + 3H₂(g)$$
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• With Dilute HCl: Forms aluminium chloride: $$2Al(s) + 6HCl(aq) \rightarrow 2AlCl₃(aq) + 3H₂(g)$$

Aluminium Oxide (Al₂O₃)

• With NaOH: Dissolves to form sodium aluminate: $$Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) \rightarrow 2NaAl(OH)₄(aq)$$
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• With Dilute HCl: Forms aluminium chloride: $$Al₂O₃(s) + 6HCl(aq) \rightarrow 2AlCl₃(aq) + 3H₂O(l)$$

Aluminium Hydroxide (Al(OH)₃)

• With NaOH: Dissolves to form sodium aluminate: $$Al(OH)₃(s) + NaOH(aq) \rightarrow NaAl(OH)₄(aq)$$
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• With Dilute HCl: Forms aluminium chloride: $$Al(OH)₃(s) + 3HCl(aq) \rightarrow AlCl₃(aq) + 3H₂O(l)$$

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2. Zinc (Zn)

Zinc Metal

• With NaOH: Reacts in hot, concentrated NaOH to form sodium zincate: $$Zn(s) + 2NaOH(aq) + 2H₂O(l) \rightarrow Na₂Zn(OH)₄(aq) + H₂(g)$$
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• With Dilute HCl: Forms zinc chloride: $$Zn(s) + 2HCl(aq) \rightarrow ZnCl₂(aq) + H₂(g)$$

Zinc Oxide (ZnO)

• With NaOH: Forms sodium zincate: $$ZnO(s) + 2NaOH(aq) + H₂O(l) \rightarrow Na₂Zn(OH)₄(aq)$$
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• With Dilute HCl: Forms zinc chloride: $$ZnO(s) + 2HCl(aq) \rightarrow ZnCl₂(aq) + H₂O(l)$$

Zinc Hydroxide (Zn(OH)₂)

• With NaOH: Dissolves to form sodium zincate: $$Zn(OH)₂(s) + 2NaOH(aq) \rightarrow Na₂Zn(OH)₄(aq)$$
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• With Dilute HCl: Forms zinc chloride: $$Zn(OH)₂(s) + 2HCl(aq) \rightarrow ZnCl₂(aq) + 2H₂O(l)$$

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3. Lead (Pb)

Lead Metal

• With NaOH: Does not react significantly under standard conditions.
• With Dilute HCl: Reacts slowly due to insoluble PbCl₂ formation: $$Pb(s) + 2HCl(aq) \rightarrow PbCl₂(s) + H₂(g)$$

Lead(II) Oxide (PbO)

• With NaOH: Forms sodium plumbite: $$PbO(s) + 2NaOH(aq) + H₂O(l) \rightarrow Na₂Pb(OH)₄(aq)$$
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• With Dilute HCl: Forms lead(II) chloride (sparingly soluble): $$PbO(s) + 2HCl(aq) \rightarrow PbCl₂(s) + H₂O(l)$$

Lead(II) Hydroxide (Pb(OH)₂)

• With NaOH: Dissolves to form sodium plumbite: $$Pb(OH)₂(s) + 2NaOH(aq) \rightarrow Na₂Pb(OH)₄(aq)$$
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• With Dilute HCl: Forms lead(II) chloride: $$Pb(OH)₂(s) + 2HCl(aq) \rightarrow PbCl₂(s) + 2H₂O(l)$$

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