Properties of P3 Oxides

• Reactions of Na and Mg with water:

  2Na(s) + 2H2O (l)--> 2NaOH(aq)+ H2(g) - Dangerous because reactants can shoot out tube

  Mg + 2H2O --> Mg(OH)2 + H2
• Period 3 Metals

  Sodium and magnesium react ionically to form positive ions

  2Na + 2H2O ---> 2NaOH + H2

  Mg + 2H2O ---> Mg(OH)2 + H2

  Sodium is more reactive than magnesium as it only has to lose one electron to form an ion, whereas magnesium has to lose two
• Magnesium with Steam

  Reaction with magnesium is slow but can be sped up using steam (instead of water) - magnesium burns with a bright white flame

  Mg + H2O (g) ---> MgO (s) + H2
• Oxides that form from P3

  Na2O: Sodium oxide is +1

  MgO: Magnesium oxide is +2

  Al2O3: Aluminium oxide is +3

  SiO2: Silicon dioxide is +4

  P4O10: Phosphorus oxide is +5

  SO2: Sulfur dioxide is +4

  SO3: Sulfur trioxide is +6

  Sulfur can also react to form SO3 with an ox state of +6 but this requires high temp & catalyst
• Structures & Bonding

  Na2O: Ionic, reactivity is vigorous

  MgO: Ionic, vigorous

  Al2O3: Ionic (covalent character), slow but faster if powdered

  SiO2: Macromolecular, slow

  P4O10: Simple covalent, vigorous

  SO2: Simple covalent, burns steadily
• Reactions with Water (Oxides)

  These ionic oxides combine with water to form alkaline solutions with pH around 10-14

  Na2O + H2O ---> 2NaOH

  MgO + H2O ---> Mg(OH)2
• Reactions with Water (Oxides)

  The simple covalent oxides of sulfur and phosphorus combine with water to form acidic solutions with a pH around ?

  P4O10 + 6H2O ---> 4H3PO4 (pH is 1)

  SO2 + H2O ---> H2SO3

  SO3 + H2O ---> H2SO4

  When in solution, these acids dissociate into H+ ions and ions of conjugate base
• Acid-Base Reactions

  Basic, ionic oxides react with acids to produce a salt and a water - neutralisation reaction

  Na2O + HCl ---> 2NaCl + H2O

  MgO + H2SO4 ---> MgSO4 +H2O

  Magnesium oxide in excess with phosphoric acid:

  3MgO + 2H3PO4 ---> Mg3(PO4)2 + 3H2O
• Acidic Covalent Oxides + Bases

  Acidic, covalent oxides react with bases to produce a salt and water - neutralisation reaction

  SiO2 + 2NaOH ---> Na2SiO3 + H2O

  P4O10 + 12NaOH ---> 4Na3PO4 + 6H2O

  SO2 + 2NaOH ---> Na2SO3 + H2O

  SO3 + 2NaOH ---> Na2SO4 + H2O
• Aluminium Oxide - Neutralisation Reactions


  Bonding in aluminium oxide is partially ionic & covalent, it is insoluble in water as ions don't dissociate (can act as an acid or base - amphoteric)

  Al2O3 + 3H2SO4 ---> Al2(SO4)3 + 3H2O

  Al2O3 + 2NaOH + 3H2O ---> 2NaAl(OH)4
• Explain (crystal structure & bonding) why silicon dioxide has a higher melting point than phosphorus oxide (4)

  SiO2 is macromolecular with strong covalent bonds so more energy is needed to overcome these bonds

  P4O10 is molecular with weak VDW forces between molecules
• Explain why the atomic radius decreases across P3, from sodium to chlorine (2)

  The nuclear charge increases and shielding is similar
• Reaction of Oxides with Air

  4P + 5O2 ---> P4O10 (white flame AND white solid)

  4Na + O2 ---> 2Na2O (yellow flame)
• (Table)

  Explain the increase in m.p from sodium oxide to magnesium oxide(2)

  Greater charge on Mg2+

  Stronger attraction between oppositely charged ions (between Mg2+ and O2-)
• Describe a method for determining the m.p of sample of phosphorus oxide and state how the result obtained could be used to evaluate its purity (3)

  Sample in Thiele tube, heat slowly and lower m.p indicates presence of impurities
• Which element forms an ionic oxide that reacts with strong alkalis?

  Aluminium
• Describe a test to distinguish between sodium oxide and phosphorus oxide: (3)

  React with water, add litmus paper - should go blue with sodium oxide and red with phosphorus oxide
• Explain why silicon dioxide has a higher m.p than sulfur trioxide (4)

  There are covalent bonds between atoms in SiO2 and VDW forces between molecules in SO3

  Covalent bonds are stronger than VDW forces and so covalent bonds take more energy to overcome
• Equation for reaction of sulfur trioxide with potassium hydroxide solution

  SO3 + 2KOH ---> K2SO4 + H2O
• Equation for reaction of magnesium oxide with phosphoric acid

  3MgO + 2H3PO4 ---> Mg3(PO4)2 + 3H2O
• Equation for the reaction of sulfur dioxide with water to form a undissociated acid

  SO2 + H2O ---> H2SO3
• Describe a test to distinguish between sodium oxide and phosphorus oxide


  Add water, add litmus paper

  Litmus paper goes blue with sodium oxide and red with phosphorus oxide solution
• Bonds V IMF

  Bonds are between atoms but IMF are between molecules