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

1. Aluminium (Al)

Aluminium Metal

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

Aluminium Oxide (Al₂O₃)

• With NaOH: Dissolves to form sodium aluminate:Al2O3(s)+2NaOH(aq)+3H2O(l)→2NaAl(OH)4(aq)Al2​O3​(s)+2NaOH(aq)+3H2​O(l)→2NaAl(OH)4​(aq)
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• With Dilute HCl: Forms aluminium chloride:Al2O3(s)+6HCl(aq)→2AlCl3(aq)+3H2O(l)Al2​O3​(s)+6HCl(aq)→2AlCl3​(aq)+3H2​O(l)

Aluminium Hydroxide (Al(OH)₃)

• With NaOH: Dissolves to form sodium aluminate:Al(OH)3(s)+NaOH(aq)→NaAl(OH)4(aq)Al(OH)3​(s)+NaOH(aq)→NaAl(OH)4​(aq)
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• With Dilute HCl: Forms aluminium chloride:Al(OH)3(s)+3HCl(aq)→AlCl3(aq)+3H2O(l)Al(OH)3​(s)+3HCl(aq)→AlCl3​(aq)+3H2​O(l)

2. Zinc (Zn)

Zinc Metal

• With NaOH: Reacts in hot, concentrated NaOH to form sodium zincate:Zn(s)+2NaOH(aq)+2H2O(l)→Na2Zn(OH)4(aq)+H2(g)Zn(s)+2NaOH(aq)+2H2​O(l)→Na2​Zn(OH)4​(aq)+H2​(g)
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• With Dilute HCl: Forms zinc chloride:Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)Zn(s)+2HCl(aq)→ZnCl2​(aq)+H2​(g)

Zinc Oxide (ZnO)

• With NaOH: Forms sodium zincate:ZnO(s)+2NaOH(aq)+H2O(l)→Na2Zn(OH)4(aq)ZnO(s)+2NaOH(aq)+H2​O(l)→Na2​Zn(OH)4​(aq)
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• With Dilute HCl: Forms zinc chloride:ZnO(s)+2HCl(aq)→ZnCl2(aq)+H2O(l)ZnO(s)+2HCl(aq)→ZnCl2​(aq)+H2​O(l)

Zinc Hydroxide (Zn(OH)₂)

• With NaOH: Dissolves to form sodium zincate:Zn(OH)2(s)+2NaOH(aq)→Na2Zn(OH)4(aq)Zn(OH)2​(s)+2NaOH(aq)→Na2​Zn(OH)4​(aq)
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• With Dilute HCl: Forms zinc chloride:Zn(OH)2(s)+2HCl(aq)→ZnCl2(aq)+2H2O(l)Zn(OH)2​(s)+2HCl(aq)→ZnCl2​(aq)+2H2​O(l)

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)→PbCl2(s)+H2(g)Pb(s)+2HCl(aq)→PbCl2​(s)+H2​(g)

Lead(II) Oxide (PbO)

• With NaOH: Forms sodium plumbite:PbO(s)+2NaOH(aq)+H2O(l)→Na2Pb(OH)4(aq)PbO(s)+2NaOH(aq)+H2​O(l)→Na2​Pb(OH)4​(aq)
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• With Dilute HCl: Forms lead(II) chloride (sparingly soluble):PbO(s)+2HCl(aq)→PbCl2(s)+H2O(l)PbO(s)+2HCl(aq)→PbCl2​(s)+H2​O(l)

Lead(II) Hydroxide (Pb(OH)₂)

• With NaOH: Dissolves to form sodium plumbite:Pb(OH)2(s)+2NaOH(aq)→Na2Pb(OH)4(aq)Pb(OH)2​(s)+2NaOH(aq)→Na2​Pb(OH)4​(aq)
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• With Dilute HCl: Forms lead(II) chloride:Pb(OH)2(s)+2HCl(aq)→PbCl2(s)+2H2O(l)Pb(OH)2​(s)+2HCl(aq)→PbCl2​(s)+2H2​O(l)