Acid base reactions between period 3 oxides and simple acids and bases. The basic oxides react with acids to make salts Na2O (s) + 2 HCl (aq) 2NaCl (aq) + H2O (l) Na2O (s) + H2SO4 (aq) Na2SO4 (aq) + H2O (l) MgO (s) + 2 HCl (aq) MgCl2 (aq) + H2O (l) Or ionically Na2O (s) + 2H+ (aq) 2Na+ (aq) + H2O (l) MgO (s) + 2 H+ (aq) Mg2+ (aq) + H2O (l) Rather than learning the equations by rote, learn the pattern. Most follow the pattern acid + base = salt + water Know the charges on the ions e.g. PO4 3- , SO4 2- Amphoteric Oxides Aluminium oxide can act as both an acid and an alkali and is therefore called amphoteric Aluminum oxide acting as a base Al2O3 (s)+ 3H2SO4 (aq) Al2 (SO4 )3 (aq) + 3H2O (l) Al2O3 + 6HCl 2AlCl3 + 3H2O Or ionically Al2O3 + 6H+ 2Al3+ + 3H2O Aluminum oxide acting as a acid Al2O3 (s)+ 2NaOH (aq) + 3H2O (l) 2NaAl(OH)4 (aq) (this equation needs learning carefully) Al2O3 (s)+ 2OH- (aq) + 3H2O (l) 2Al(OH)4 – (aq) SiO2 has a giant covalent structure with very strong bonds. This stops SiO2 dissolving or reacting with water and weak solutions of alkali. It will, however, react with very concentrated NaOH 2NaOH (l) + SiO2 (s) Na2SiO3 (aq) + H2O It is still classed as an acidic oxide The other simple molecular acidic oxides react with bases to form salts. P4O10 (s) + 12 NaOH (aq) 4Na3PO4 (aq) + 6 H2O (l) P4O10 + 6 Na2O 4Na3PO4 SO2 (g) + 2NaOH (aq) Na2SO3 (aq) + H2O (l) SO3 (g) + 2NaOH(aq) Na2SO4 (aq) + H2O (l) Or show ionically P4O10 (s) + 12 OH- (aq) 4PO4 3-(aq) + 6 H2O (l) SO2 (g) + 2OH- (aq) SO3 2- (aq) + H2O (l) SO3 (g) + 2OH- (aq) SO4 2- (aq) + H2O (l) Be careful for whether the question is asking for an ionic equation or a full one
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3.2.4 Properties of Period 3 elements and their oxides (A-level only)
Students should be able to:
• write equations for the reactions that occur between the oxides of the elements Na–S and given acids and bases.