Edexcel IGCSE Chemistry: Principles of Chemistry — Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Principles of Chemistry revision notes

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Section A

1. Describe the arrangement and movement of particles in a solid, a liquid and a gas. [3]

2. Define an isotope, and explain why isotopes of an element have identical chemical properties. [3]

3. State what is meant by ionic bonding. [2]

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Section B

4. A long glass tube has cotton wool soaked in concentrated ammonia at one end and cotton wool soaked in concentrated hydrochloric acid at the other. After a few minutes a white ring forms.

(a) Name the white solid. [1]

(b) State and explain where the ring forms relative to the centre of the tube. [3]

(c) State and explain the effect of raising the temperature. [2]

5. Sodium chloride and iodine have very different melting points (801 °C and 114 °C).

(a) Describe the structure and bonding in each. [4]

(b) Explain the difference in melting point. [3]

(c) Explain why solid sodium chloride does not conduct electricity but molten sodium chloride does. [2]

6. Concentrated aqueous sodium chloride is electrolysed with inert electrodes.

(a) Identify the product at each electrode. [2]

(b) Write the half-equation at the cathode. [1]

(c) Explain why hydrogen is produced rather than sodium. [2]

7. 4.6 g of sodium reacts completely with chlorine. (A_r: Na = 23, Cl = 35.5)

(a) Calculate the moles of sodium. [1]

(b) Calculate the mass of sodium chloride formed. [3]

Section C

8. Describe the structure and bonding in a metal, and explain why metals conduct electricity. [3]

9. Diamond and graphite are both giant covalent structures of carbon, but only graphite conducts electricity.

(a) Explain why both have very high melting points. [2]

(b) Explain why graphite conducts but diamond does not. [3]

10. 24.0 g of magnesium burns completely in oxygen. (A_r: Mg = 24, O = 16)

(a) Write the balanced symbol equation. [1]

(b) Calculate the mass of magnesium oxide formed. [3]

11. A compound contains 40.0 g of calcium, 12.0 g of carbon and 48.0 g of oxygen. (A_r: Ca = 40, C = 12, O = 16). Calculate its empirical formula. [3]

12. (a) State what is meant by the atomic number of an element. [1]

(b) Chlorine has two isotopes, chlorine-35 and chlorine-37. State one way in which the atoms of these isotopes are different and one way in which they are the same. [2]

13. Explain why magnesium, a metal, can be hammered into shape without breaking. [2]

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Answers

1. Solid: regular close-packed arrangement, particles vibrate about fixed positions [1]. Liquid: close together but irregular, particles slide past one another [1]. Gas: far apart and random, particles move rapidly in all directions [1].

2. Atoms of the same element with the same number of protons but different numbers of neutrons [1]. Chemical properties depend on the arrangement of electrons [1], which is identical because the proton number — and hence electron number — is the same [1].

3. The electrostatic attraction [1] between oppositely charged ions [1].

4. (a) Ammonium chloride (NH₄Cl) [1].

(b) Nearer the hydrochloric acid end [1]. Ammonia has a lower relative molecular mass (17 vs 36.5) [1], so its particles diffuse faster and travel further before the gases meet [1].

(c) The ring forms faster [1], because the particles have more kinetic energy and move faster, so they diffuse more quickly [1].

5. (a) NaCl: giant ionic lattice [1] of Na⁺ and Cl⁻ ions held by strong electrostatic attractions [1]. Iodine: simple molecular [1], I₂ molecules held together by weak intermolecular forces [1].

(b) Melting NaCl requires overcoming many strong electrostatic attractions throughout the lattice [1], needing a large amount of energy [1]. Melting iodine only requires overcoming weak intermolecular forces between molecules — the covalent bonds within I₂ are not broken [1].

(c) In the solid the ions are held in fixed positions and cannot move [1]. When molten, the ions are free to move and carry charge [1].

6. (a) Cathode: hydrogen [1]. Anode: chlorine [1].

(b) 2H⁺ + 2e⁻ → H₂ (or 2H₂O + 2e⁻ → H₂ + 2OH⁻) [1].

(c) Sodium is more reactive than hydrogen [1], so hydrogen ions are discharged in preference [1].

7. (a) n = 4.6 ÷ 23 = 0.20 mol [1].

(b) 2Na + Cl₂ → 2NaCl, so n(NaCl) = 0.20 mol [1]. M_r(NaCl) = 23 + 35.5 = 58.5 [1]. m = 0.20 × 58.5 = 11.7 g [1].

8. A metal is a lattice of positive ions in a sea of delocalised electrons [1]. It conducts because the delocalised electrons are free to move through the structure and carry charge [1], which is also why metals are malleable — the layers of ions can slide without breaking any specific bond [1].

9. (a) Both are giant covalent structures held together by a network of strong covalent bonds throughout the lattice, and melting requires breaking a very large number of these strong bonds, needing a large amount of energy [2].

(b) In graphite, each carbon atom bonds to only three others, leaving one delocalised electron per atom free to move and carry charge [2]. In diamond, each carbon bonds to four others, so all outer electrons are held in covalent bonds and none are free to move [1].

10. (a) 2Mg + O₂ → 2MgO [1].

(b) n(Mg) = 24.0 ÷ 24 = 1.0 mol [1]; ratio Mg : MgO is 2 : 2, so n(MgO) = 1.0 mol; M_r(MgO) = 24 + 16 = 40 [1]; mass = 1.0 × 40 = 40.0 g [1].

11. moles: Ca = 40.0 ÷ 40 = 1.0; C = 12.0 ÷ 12 = 1.0; O = 48.0 ÷ 16 = 3.0 [1]. Dividing through by the smallest (1.0) gives the ratio Ca : C : O = 1 : 1 : 3 [1]. Empirical formula: CaCO₃ [1].

12. (a) The number of protons in the nucleus of an atom [1]. (b) Different: chlorine-37 has two more neutrons (20 instead of 18) [1]. Same: the same number of protons (17) (or electrons, so the same chemical properties) [1].

Mark-scheme insight (Pearson Edexcel 4CH1 June 2024 mark scheme, Paper 1CR, Question 1(b)(i)): atomic number is credited as the number of protons; protons plus neutrons is the mass number, which is credited in the next part. Try the real question next: Pearson Edexcel International GCSE Chemistry 4CH1, June 2024, Paper 1CR, Question 1.

Source for the mark-scheme insights on this page: Pearson Edexcel International GCSE Chemistry 4CH1 Paper 1CR mark scheme (Summer 2024) and Pearson Edexcel International GCSE Chemistry 4CH1 Paper 2CR mark scheme (Summer 2024), paraphrased.

13. Magnesium has layers of positive ions held together by delocalised electrons [1]. The layers (of ions) can slide over one another while the metallic bonding still holds them together [1].

Mark-scheme insight (Pearson Edexcel 4CH1 June 2024 mark scheme, Paper 2CR, Question 3(a)(ii)): the marks are for layers of atoms or ions (particles is also allowed) that slide over one another; answers that bring in intermolecular forces are rejected. In the part before, “protons” was rejected as the name for the positive particles. Try the real question next: Pearson Edexcel International GCSE Chemistry 4CH1, June 2024, Paper 2CR, Question 3.

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Where marks are usually lost

• Saying covalent bonds break when iodine melts.
• Saying ionic solids conduct electricity.
• Explaining the diffusion ring position without reference to relative molecular mass.
• Omitting “electrostatic attraction” from the ionic bonding definition.
• Working from mass ratios instead of converting to moles first.