IGCSE Chemistry Past Papers
Topic 2.4.5: Properties of Ionic Compounds
Exam Focus: Papers 2, 4 & 6 Style Questions
15 Questions • 38 Total Marks • Mark Schemes Included
Exam Strategy Guide
Section A: Melting Points
- • Always mention "electrostatic forces"
- • Link high charge → stronger forces
- • Don't say "bonds" - say "forces"
Section B: Conductivity
- • Solid: ions FIXED in lattice
- • Molten/Aqueous: ions FREE to move
- • Ions carry charge (not electrons!)
Section C: Scenarios
- • Pattern: High MP + conducts when molten = IONIC
- • Elimination method for identification
- • Describe experimental METHOD clearly
Common Mistakes
- • ❌ "Strong bonds" → ✅ "Strong electrostatic forces"
- • ❌ "Free electrons" → ✅ "Free ions"
- • ❌ "Has ions" → ✅ "Ions free to move"
Section A: Melting Points (10 marks)
Question A1
[2 marks]Sodium chloride has a melting point of 801°C. Explain why ionic compounds have high melting points.
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Question A2
[3 marks]Magnesium oxide (MgO) has a melting point of 2852°C, much higher than sodium chloride (801°C). Suggest why magnesium oxide has a higher melting point than sodium chloride.
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Question A3
[2 marks]A student heats a white solid. It does not melt even when heated strongly with a Bunsen burner. What does this suggest about the bonding in the solid?
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Question A4
[3 marks]Potassium bromide melts at 734°C. Describe what happens to the structure of potassium bromide when it melts.
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Question A5
[2 marks]Explain why energy is required to melt an ionic compound.
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Section B: Electrical Conductivity (13 marks)
Question B1
[2 marks]Explain why solid sodium chloride does not conduct electricity.
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Question B2
[2 marks]Explain why molten sodium chloride conducts electricity.
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Question B3
[3 marks]Aqueous sodium chloride solution conducts electricity. Explain why, and state which particles carry the charge.
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Question B4
[4 marks]A student sets up a circuit with a bulb and two electrodes. When the electrodes are placed in solid lead(II) bromide, the bulb does not light. When the solid is heated and melts, the bulb lights up. Explain these observations.
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Question B5
[2 marks]During electrolysis of molten sodium chloride, sodium is formed at the negative electrode. Explain why sodium ions move towards the negative electrode.
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Section C: Scenarios & Identification (15 marks)
Question C1
[1 mark]Substance X has a high melting point and conducts electricity when dissolved in water. What type of bonding is present in substance X?
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Question C2
[3 marks]The table shows properties of four substances. | Substance | Melting Point | Conducts as solid? | Conducts when molten? | |-----------|---------------|--------------------|-----------------------| | A | 801°C | No | Yes | | B | -78°C | No | No | | C | 1538°C | Yes | Yes | | D | 3550°C | No | No | Identify the ionic compound and explain your answer.
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Question C3
[2 marks]A compound conducts electricity when molten but not when solid. Explain what this tells you about the structure of the compound.
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Question C4
[4 marks]Calcium chloride (CaCl₂) is an ionic compound. (a) Explain why calcium chloride has a high melting point. [2] (b) Describe an experiment to show that calcium chloride conducts electricity when molten. [2]
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Question C5
[5 marks]A student has four white solids: sugar (C₁₂H₂₂O₁₁), sodium chloride (NaCl), silicon dioxide (SiO₂), and magnesium (Mg). Describe how the student could use melting point and electrical conductivity tests to identify which solid is sodium chloride.
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🎯 Exam Technique Reminder
For 2-mark questions: Make TWO distinct points. For 3-mark questions: Make THREE distinct points. Never repeat yourself!
High Melting Point?
Strong electrostatic forces + Large energy needed
Conducts When Molten?
Ions free to move + Can carry charge
Identify Ionic?
High MP + Conducts only when molten/dissolved
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