Reaction of oxides with water

• The basic oxides

  Equations

  Na2O (s) + H2O (l) --> 2Na+ + 2OH-(aq)

  • pH is between 13-14

  MgO (s) + H2O(l) --> Mg(OH)2 (aq)

  • pH is between 9-10 due to Mg(OH)2 being sparingly soluble so its a weak alkaline
• The insoluble oxides

  Aluminium and silicon oxides are both insoluble in water and so the pH doesn't change and remain 7
• The acidic oxides

  Equations

  P4O10 (s) + 6H2O ---> 4H3PO4 (aq)

  • Forms a strong triprotic acid
  • pH is between 1-2

  SO2(g) + H2O (l) --> H2SO3 (aq)

  • Forms a slightly weaker acid called sulfurous acid can also be called sulfuric (|V) acid
  • pH is between 2-3

  SO3(g) + H2O (l) ---> H2SO4 (aq)

  • Sulfur trioxide reacts violently with water
  • Forms a strong acid with a pH between 0-1