AQA A2 Chemistry C22 Periodicity

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C22.1 Reactions of Period 3 elements AQA A2 Chemistry C22 Periodicity Kerboodle Answers: Page No. 94

1 They are malleable (can be beaten into sheets) and ductile (can be drawn inro wires). They aregood conductors of heat. 2 They tend to be brittle -they are poor conductors of heat. 3 a +1 b What is unusual about this? -1. Oxidation state of oxygen is usually -2. c C +2-2+1 Mg(OH)₂ = + 2 + 2 (-2 + 1) = 0 4 +4

22.2 The oxides of elements in Period 3 AQA A2 Chemistry C22 Periodicity Kerboodle Answers : Page No. 98

1 Na₂O(s) + H₂O(1) — 2NaOH(aq) b i Before+1, after+1 ii Neither 2 a OH^–ions b What range of pH values represents an alkaline solution? Greater than 7 3 Phosphorus forms another oxide, P 406. a Acidic

It is a non-metal c P₄O₆(s) + 6H₂O(1) →4H₃PO₃(aq)

22.3 The acidic/basic nature of the Period 3 oxides AQA A2 Chemistry C22 Periodicity Kerboodle Answers : Page No. 100

1 a Na₂O(s) + 2HCI(aq) →2NaCI(aq) + H₂O(1) b Magnesium oxide with sulfuric acid MgO(s) + H₂SO₄(aq) →MgSO₄(aq) + H₂O(1) c Aluminium oxide with nitric acid. AI₂O₃(s) + 6HNO₃(aq) → 3H₂O(I) + 2Al(NO₃)₃(aq) 2 a +4 -2           +1 -2 +1            +1 +4-2         +1 -2 SiO₂(S) + 2NaOH(aq) → Na₂SiO₃(aq) + H₂O(1) b Is the reaction a redox reaction? No c Explain your answer to b. No change in oxidation number of any of the elements occurs 3 P₄O_l0(s) + 6H₂O(1) →4H ₃PO₄(aq) Banner 2

Practice questions: Page No. 101-103

1 (a) Charge on oxide ion bigger than on chloride or oxide ion smaller than chloride or charge density on oxide ion greater than chloride Therefore electrostatic attraction is stronger (b) MgO (is a white solid that) forms a suspension (or slightly soluble) MgO + H₂O → Mg(OH)₂ or → Mg₂+ + 2OH pH is 8 to 10 (c) SO2 dissolves or forms (colourless) solution SO2 + H2O → H2SO3 or → H⁺ + H₂SO₃− or → 2H⁺ + SO₃^2- pH is 1 to 4 2 Na₂O: vigorous or exothermic reaction; or forms a colourless solution, pH of solution formed is 13 or 14. Na₂O + H2O → 2NaOH P₄O₁₀ or P₂O₅: vigorous or exothermic reaction; or forms a colourless solution, pH of solution formed is 0 or 1. P₄O₁₀ + 6H₂O → 4H₃PO₄ 3 (a) (i) Ionic (ii) Sodium (iii) Na₂O + H₂O → 2NaOH (b) (i) Covalent (ii) Phosphorus (iii) H₃PO₄ (c) (i) Macromolecular (ii) Silicon (iii) e.g., CaO + SiO₂ → CaSiO₃ 4  (a) (i) P₄O₁₀ or SO₃ (ii) Na₂O (b) (i) MgO and HNO₃ MgO + 2HNO₃ → Mg(NO₃)₂ + H₂O (ii) SiO₂ and NaOH 2NaOH + SiO₂ → Na₂SiO₃ + H₂O (iii) Na₂O and H₃PO₄. (3 marks) 3Na₂O + 2H₃PO₄ → 2Na₃PO₄ + 3H₂O (c) P₄O₁₀ is molecular or simple covalent. This means that there are weak intermolecular forces between molecules. SiO2 is a macromolecule or giant covalent molecule. Many strong covalent bonds must be broken. 5 (a) Sodium oxide Na₂O + H₂O → 2NaOH pH = 14 (b) Sulfur dioxide. (2 marks) AQA, 2003 SO₂ + H₂O → H₂SO₃ pH = 1–3 6 (a) (i) P is Na₂O or sodium oxide. Ionic Ions are not free to move in the solid state. Ions are free to move when molten or in aqueous solution. Na₂O + H₂O → 2NaOH (ii) Q is SO2 or sulfur dioxide. Covalent Intermolecular forces are weak or van der Waals forces are weak. SO₂ + H₂O → H₂SO₃ (b) (i) . Amphoteric (ii) . Al(OH)₃ + NaOH → NaAl(OH)₄ 2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O (iii) Suggest why R is insoluble in water. (6 marks) AQA 2002

• Large lattice energy;
• Strong covalent bonds;
• ΔHsoln is very positive;
• ΔG is very positive;
• The sum of the hydration energies is less than the covalent bond energies.

7 (a) White powder / solid / ash / smoke Bright / white light / flame Mg + H₂O → MgO + H₂ (b) Mg2⁺ / magnesium ion has higher charge than Na+ Attracts delocalised / free / sea of electrons more strongly / metal–metal bonding stronger / metallic bonding stronger (c) Structure: Macromolecular / giant molecule / giant covalent Bonding: Covalent / giant covalent Physical Properties:

• Hard
• Brittle / not malleable
• Insoluble
• Non conductor

(d) Formula: P₄O₁₀ Structure: Molecular Bonding: Covalent / shared electron pair Van der Waals’ / dipole–dipole forces between molecules (e) Write an equation for this reaction. (1 mark) SO₂ + H₂O → H⁺ + HSO₃^– (f) P₄O₁₀ + 6MgO → 2Mg₃(PO₄)₂ 8 (a) Outline a simple experiment to demonstrate that magnesium oxide has this type of bonding. (3 marks) MgO is ionic Melt it (Molten oxide) conducts electricity (b)) Macromolecular Covalent bonding Water cannot (supply enough energy to) break the covalent bonds / lattice (c) (Phosphorus pentoxide’s melting point is) lower Molecular with covalent bonding Weak / easily broken / not much energy to break intermolecular forces OR weak van der Waals / dipole-dipole forces of attraction between molecules (d) Reagent (water or acid) Equation, e.g., MgO + 2HCl → MgCl₂ + H₂O (e) P₄O₁₀ + 12NaOH → 4Na₃PO₄ + 6H₂O 9 (a) To prevent it coming into contact/reacting with oxygen/air (b) One molecule contains 4P and 10O/the molecular formula is P₄O₁₀ (c) P₄O₁₀ is a bigger molecule (than SO3)/greater Mr/more electrons/ greater surface area Van der Waals / vdW forces between molecules are stronger/require more energy to break (d) P₄O₁₀ + 6H₂O → 4H₃PO₄ pH must be in the range −1 to +2 (e) (i) 3MgO + 2H₃PO₄→ Mg₃(PO₄)₂ + 3H₂O (ii)) MgO is sparingly soluble/insoluble/weakly alkaline (iii) An excess of NaOH would make the lake alkaline/toxic/kill wildlife. Banner 3

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