2.4 Period 3

• Which metals in period 3 react with water?

  Sodium and Magnesium
• Describe and give an equation for the reaction of sodium with water.

  -Reacts vigorously with water to form an alkaline solution

  -Sodium floats as it is less dense than water

  -Fizzes as a gas is produced

  -Molten due to the heat given off during the reaction therefore exothermic

  -Orange flame

  
  

  2Na(s) + H2O(l) —> 2NaOH(aq) + H2(g)
• How does magnesium react with cold water? Give an equation.

  -very slowly and forms a slightly alkaline solution

  
  

  Mg(s) + H2O(l) —> Mg(OH)2(aq) + H2(g)
• How does magnesium react with steam? Give an equation.

  Vigorously and produces a bright white light

  
  

  Mg(s) + H2O(g) —> MgO(s) + H2(g)
• Why does sodium react more vigorously than magnesium?

  -lower nuclear charge

  -larger atomic radius

  -loses electrons more easily
• How does chlorine react with water? Give an equation.

  Disproportionation reaction (Cl2 both oxidised and reduced) and produces a pale yellow solution

  
  

  Cl2 + H2O —> HClO + HCl
• What observation occurs when sodium reacts with oxygen? Give an equation.

  Burns with orange flame

  
  

  4Na + O2 —> 2Na2O
• What observation occurs when magnesium reacts with oxygen? Give an equation.

  Burns with white flame

  
  

  2Mg + O2 —> 2MgO
• What observation occurs when aluminium reacts with oxygen? Give an equation.

  Burns with white flame

  
  

  4Al + 3O2 —> 2Al2O3
• What observation occurs when silicon reacts with oxygen? Give an equation.

  Burns with white flame

  
  

  Si + O2 —> SiO2
• What observation occurs when phosphorus reacts with oxygen? Give an equation.

  Burns with white flame

  
  

  P4 + 5O2 —> P4O10
• What observation occurs when sulphur reacts with oxygen? Give an equation.

  Burns with blue flame

  
  

  S8 + 8O2 —> 8SO2
• What are the ionic oxides in period 3?

  Na2O, MgO and Al2O3
• Why do MgO and Al2O3 have higher melting points than Na2O?

  Na+ has a larger ionic radius and lower ionic charge therefore electrostatic attraction to O2- is weaker
• Why is the melting point of Al2O3 lower than that of MgO?

  Al3+ has a large charge to size ration so can polarise O2-. Al2O3 displays a degree of covalent character
• How does Al2O3 display covalent character?

  Al3+ has a high charge and small size therefore it is able to pulled electron density towards itself and polarise the O2- ion.

  O2- has a large size and large negative charge so the electron density is distorted by Al3+
• What is SiO2 and why does it have a higher melting point?

  Macromolecular - high MP as need to break strong covalent bonds
• What are P4O10, SO2 and SO3 and why do they have a low melting point?

  Molecular covalent - need to break weak intermolecular forces between molecules
• Explain the decrease in melting point of the molecular oxides.

  Size of the molecules decrease, therefore less electrons, therefore weaker Van der Waal's forces
• How do ionic oxides react with water?

  Produce hydroxide ions and therefore are bases
• How does Na2O react with water? Give an equation.

  It is very soluble so produces many OH- ions therefore pH is approximately 14

  
  

  Na2O + H2O —> NaOH
• How does MgO react with water? Give an equation.

  Slightly soluble so few OH- ions are formed therefore pH is approximately 10

  
  

  MgO + H2O —> Mg(OH)2
• How does Al2O3 react with water?

  It is insoluble in water so no OH-ions are formed and therefore pH of water is unaffected so pH remains approximately 7
• Does SiO2 react with water?

  SiO2 is macromolecular therefore is very stable so it is insoluble in water as there is a small difference in electronegativity between Si and O so there is minimal attraction to the water molecules
• How does P4O10 react with water? Give an equation.

  Reacts vigorously to form phosphoric acid pH 0-1

  
  

  P4O10 + 6H2O —> 4H3PO4
• How does SO2 react with water? Give an equation.

  Reacts to form sulphurous acid pH 2 -4

  
  

  SO2 + H2O —> H2SO3q
• How does SO3 react with water? Give an equation.

  Reacts to form sulphuric acid pH 1 - 3

  
  

  SO3 + H2O —> H2SO4
• How do Na2O and MgO react with hydrochloric acid?

  Na2O + 2HCl —> 2NaCl + H2O

  MgO + 2HCl —> MgCl2 + H2O
• How do Na2O and MgO react with sulphuric acid?

  Na2O + H2SO4 —> Na2SO4 +H2O

  MgO + H2SO4 —> MgSO4 + H2O
• How do Na2O and MgO react with nitric acid?

  Na2O + 2HNO3 —> 2NaNO3 + H2O

  MgO + 2HNO3 —> Mg(NO3)2 + H2O
• How does Al2O3 react with hydrochloric acid?

  Al2O3 + 6HCl —> 2AlCl3 + 3H2O
• How does Al2O3 react with sulphuric acid?

  Al2O3 + 3H2SO4 —> Al2(SO4)3 + 3H2O
• How does Al2O3 react with nitric acid?

  Al2O3 + 6HNO3 —> 2Al(NO3)3 + 3H2O
• How does Al2O3 react with sodium hydroxide?

  Al2O3 + 2NaOH —> 2NaAlO2 + 2H2O
• How does SiO2 react with NaOH and why?

  SiO2 will act as a weak acid and therefore react with a strong base, under certain conditions

  
  

  SiO2 + 2NaOH —> Na2SiO3 + H2O
• How does P4O10 react with NaOH?

  P4O10 + 12NaOH —> 4Na3PO4 + 6H2O
• How does SO2 react with NaOH?

  SO2 + 2NaOH —> Na2SO3 + H2O
• How does SO3 react with NaOH?

  SO3 + 2NaOH —> Na2SO4 + H2O