Reactions3.1.3

Chemical Properties of Period 3 Oxides

Tracing the shift from Basic (Ionic) to Acidic (Covalent) character.

Element	Formula	Bonding	Nature	Reaction w/ Water	pH
Na	$Na_2O$	Ionic	Basic	$Na_2O + H_2O \to 2NaOH$	~14
Mg	$MgO$	Ionic	Basic	$MgO + H_2O \to Mg(OH)_2$	~9
Al	$Al_2O_3$	Ionic*	Amphoteric	Insoluble	-
Si	$SiO_2$	Giant Cov.	Acidic	Insoluble	-
P	$P_4O_{10}$	Molecular	Acidic	$P_4O_{10} + 6H_2O \to 4H_3PO_4$	~2
S	$SO_3$	Molecular	Acidic	$SO_3 + H_2O \to H_2SO_4$	~1

The Special Case: Aluminum Oxide

Aluminum oxide is amphoteric, meaning it can react as both an acid and a base. Its insolubility in water means pH isn't directly relevant, but its reactivity proves its dual nature.

Acting as a Base

Reacts with warm, dilute acid:

Al_2O_3 + 6HCl \to 2AlCl_3 + 3H_2O

Acting as an Acid

Reacts with hot, concentrated alkali:

Al_2O_3 + 2NaOH + 3H_2O \to 2NaAl(OH)_4

(Sodium Aluminate)

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