Inorganic 2 Section 2 - Unit 22: Periodicity
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Deduce the type of bonding in phosphorus oxide (1 mark)
Simple molecular
Write an equation for the reaction between phosphorus oxide and water (1 mark)
P₄O₁₀ + 6H₂O → 4H₃PO₄
State the meaning of the term amphoteric (1 mark)
Reacts with acids and bases
Explain why sodium oxide forms an alkaline solution when it reacts with water (2 marks)
• Sodium oxide contains O²⁻ ions - Which react with water forming OH– ions
Write two equations to show the amphoteric nature of aluminium oxide (2 marks)
Al₂O₃(s) + 2OH⁻ (aq) + 3H₂O (l) → 2Al(OH)₄ (acid) Al₂O₃ + 6HCl → 2Al³⁺ + 6Cl⁻ + 3H₂O
Write an ionic equation for the reaction of phosphorus(V) oxide with an excess of sodium hydroxide solution (1 mark)
P₄O₁₀ + 12OH⁻ → 4PO₄³⁻ + 6H₂O
Describe what you would observe when magnesium is heated with steam (2 marks)
• White solid - White light / flame
Describe what you would observe when sodium is heated in oxygen (2 marks)
• White solid - Yellow flame
State the observation when magnesium reacts with oxygen (2 marks)
• Burns with a white flame - To give a white solid smoke
State the observation when aluminium reacts with oxygen (2 marks)
• Burns with a white flame - To give a white solid smoke
State the observation when silicon reacts with oxygen (2 marks)
• Burns with a white flame - To give a white solid smoke
State the observation when phosphorus reacts with oxygen (2 marks)
• Burns with a white flame - To give a white solid smoke
State the observation when sulfur reacts with oxygen (2 marks)
• Burns with a blue flame - To produce an acidic choking gas
Explain why aluminium oxide shows some covalent character as well as ionic character (2 marks)
• Small aluminium ion has high charge (3+) so pulls the electrons from O²- towards itself • This distorts the oxide charge cloud and creates covalent character
Suggest why P₄O₁₀ and SO₂ are simple covalent oxides (1 mark)
• Small electronegativity difference between the non-metal and the O atoms
Suggest and explain how aluminium metal is protected from corrosion in moist air (3 marks)
• Thin layer of aluminium oxide • As it has a high lattice strength and is insoluble in water • So makes this layer impermeable to air and water
State the pH of the solution formed when sodium oxide reacts with water and explain why it has this pH (2 marks)
• pH 13 - Oxide ions accept protons and become hydroxide ions
State the pH of magnesium hydroxide and suggest why it is lower than the pH of sodium hydroxide (3 marks)
• pH 9 • It’s lattice is stronger so it is only slightly soluble in water • So fewer OH- ions are produced
State the pH of the solution formed when phosphorus oxide reacts with water (1 mark)
• pH 0
State the pH of H₂SO₃ (1 mark)
pH 3
State the pH of H₂SO₄ (1 mark)
pH 0
State the ionic equation in which aluminium oxide acts as a base (1 mark)
Al₂O₃ + 6H+ –> 2Al³+ + 3H₂O
State the ionic equation in which aluminium oxide acts as an acid (1 mark)
Al₂O₃ + 2OH- + 3H₂O –> 2Al(OH)₄-
Explain why magnesium has a higher melting point than sodium (2 marks)
• Magnesium has a higher charge - So delocalised electrons pulled in more closely