Edexcel IGCSE Chemistry: Principles of Chemistry — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — 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]

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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].

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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.