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3.1.6Additional lessons

Metallic and Non-Metallic Oxides — IB Chemistry SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 42 of 98

📚 IB Chemistry SL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 6Metal Oxides

Position in the periodic table decides whether an oxide is acidic or basic.

General behaviour
  • General behaviour Oxides of metals are ionic and usually basic, reacting with acids to form salts and water.
Sodium oxide
  • Sodium oxide Na₂O dissolves in water to give a strongly alkaline solution: Na₂O(s) + H₂O(l) → 2NaOH(aq).
Magnesium oxide
  • Magnesium oxide MgO is only slightly soluble, giving a weakly alkaline solution of Mg(OH)₂.
Neutralisation
  • Neutralisation A basic oxide reacts with acid, as in MgO(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l).

Part 2 of 6Non-Metal Oxides

Non-Metal Oxides
General behaviour
  • General behaviour Oxides of non-metals are covalent and usually acidic, forming acids with water.
Sulfur dioxide
  • Sulfur dioxide SO₂(g) + H₂O(l) → H₂SO₃(aq), a weak acid.
Sulfur trioxide
  • Sulfur trioxide SO₃(g) + H₂O(l) → H₂SO₄(aq), a strong acid.
Phosphorus(V) oxide
  • Phosphorus(V) oxide P₄O₁₀(s) + 6H₂O(l) → 4H₃PO₄(aq), phosphoric acid.
OxideType of bondingNature
Na₂Oionicbasic
MgOionicbasic
Al₂O₃ionic with covalent characteramphoteric
SiO₂giant covalentweakly acidic
P₄O₁₀, SO₃covalent molecularacidic

Part 3 of 6Amphoteric Oxides

1
Aluminium oxide lies between the basic and acidic oxides in period 3.
2
It reacts with acid as a base: Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l).
3
It also reacts with strong alkali as an acid: Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2Na[Al(OH)₄](aq).
4
A substance that shows both types of behaviour is called amphoteric.
5
Moving across period 3 the oxides therefore change from basic through amphoteric to acidic.

Part 4 of 6Acid Deposition

Sulfur dioxide
  • Sulfur dioxide Burning fossil fuels containing sulfur releases SO₂, which dissolves in cloud water to form acidic solutions.
Nitrogen oxides
  • Nitrogen oxides NO₂ from vehicle engines reacts with water and oxygen to form nitric acid: 4NO₂(g) + O₂(g) + 2H₂O(l) → 4HNO₃(aq).
Effects
  • Effects Acid rain damages forests, lowers the pH of lakes and corrodes limestone and metal structures.
Carbon dioxide
  • Carbon dioxide CO₂ dissolves in water to form a weak acid, so natural rain has a pH of about 5.6.

Part 5 of 6Worked Example

Question Write balanced equations for the reaction of phosphorus(V) oxide with water and for sulfur trioxide with water, and state whether each oxide is acidic or basic.

  1. Phosphorus(V) oxideP₄O₁₀(s) + 6H₂O(l) → 4H₃PO₄(aq).
  2. Sulfur trioxideSO₃(g) + H₂O(l) → H₂SO₄(aq).
  3. Both form acids with water, so both are acidic oxides.

Answer Both oxides are acidic: P₄O₁₀ gives H₃PO₄ and SO₃ gives H₂SO₄.

Part 6 of 6Exam Checklist & Tips

3.1.6 – Key Points for the Exam

  • Basic oxide An oxide, usually of a metal, that reacts with acids to form a salt and water.
  • Acidic oxide An oxide, usually of a non-metal, that reacts with water or alkalis to form acidic solutions.
  • Amphoteric Able to react as both an acid and a base.
  • Acid deposition Acidic substances from the atmosphere deposited on land and water.

Common Mistakes

  • Writing the product of SO₂ and water as H₂SO₄ instead of H₂SO₃.
  • Saying all oxides are acidic.
  • Forgetting that Al₂O₃ is amphoteric.
  • Describing MgO as very soluble in water.

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