Acid/base nature of the period 3 oxides

• Basic oxides

  Since both sodium and magnesium are both basic they can react with acids to produce a salt and water.

  Equations:

  • Na2O(s) + H2SO4 (aq) --> Na2SO4 (aq) + H2O(l)
  • MgO (s) +2HCl (aq) ---> MgCl2(aq) + H2O(l)
• Amphoteric oxides

  They can act as an acid or base.

  Equations

  Al2O3 (s) + 6HCl (aq) --> 2AlCl3 (aq) + 3H2O (l)

  • Acts as a base

  Al2O3(s) + 2NaOH (aq) + 3H2O (l) --> 2NaAl(OH)4 (aq)

  • Acts as an acid
  • Requires hot and concentrated sodium hydroxide

  SiO2 (s) + 2NaOH (aq) --> Na2SiO3 (aq) + H2O (l)

  • NaOH has to be hot and concentrated.
  • Acts as an acid

  SiO2(s) + 4HF (aq) --> SiF4 (aq) + 2H2O(l)

  • Acts a base to HF (strong acid)
• Acidic oxides

  When P4O10 is added to an alkaline solution it first reacts with water to form phosphoric acid which then reacts with the base to form the following equations if there is an excess of base.

  • H3PO4 + NaOH(aq) --> NaH2PO4 (aq) + H2O (l)
  • NaH2PO4 + NaOH (aq) --> Na2HPO4 (aq) + H2O (l)
  • Na2HPO4 + NaOH(aq) ---> Na3PO4(aq) + H2O (l)

  Overall equation is:

  H3PO4 + 3NaOH --> Na3PO4 (aq) + 3H2O

  The reaction starting with P4O10 as the reactant would look like:

  P4O10 + 12NaOH --> 4Na3PO4 (aq) + 6H2O
• Acidic oxides pt2

  Sulfur oxides reacts with NaOH to form:

  • SO2 (aq) + NaOH (aq) --> NaHSO3 (aq)

  Then the sodium hydrogen sulfate reacts with NaOH to form sodium sulfate

  • NaHSO3 (aq) + NaOH (aq) --> Na2SO3 (aq) +H2O (l)

  Overall reaction:

  • SO2 (aq) + 2NaOH (aq) --> Na2SO3 (aq) + H2O (l)
• Due to some oxides being bases and others acids they can react in an acid-base reaction e.g.

  • P4O10 +6Na2O --> 4Na3PO4 (aq)
  • P4O10 +6MgO ---> 2Mg3(PO4)2 (aq)