OxfordAQA International GCSE Chemistry: How bonding and structure are related to the properties of substances (9202) – 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 from your board or school.

Every question here targets section 3.2.2 of OxfordAQA’s International GCSE Chemistry (9202) specification (Version 6.2, applying to exams May/June 2018 onwards): how bonding and structure are related to the properties of substances, statements a to g. The qualification is untiered, so every question is for all candidates. Where data are given, use the values in the question.

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Questions

1. Molten lithium bromide conducts electricity. Explain why. [2]

2. Three structure diagrams are described below. For each one, state the type of structure shown.

• Diagram A: groups of four phosphorus atoms, each group joined by lines into a small tetrahedron, with empty space between the groups.
• Diagram B: a regular grid of particles labelled Li⁺ and F⁻, alternating along every row and column.
• Diagram C: silicon atoms, each joined by lines to four other silicon atoms, with bonds running off every edge of the drawing.

[3]

3. Use these values.

Substance	Melting point / °C	Boiling point / °C	Conducts as solid?	Conducts when molten?
J	−95	69	No	No
K	772	1935	No	Yes
L	1538	2862	Yes	Yes
M	1650	2230	No	No

(a) Identify the type of structure of each substance J, K, L and M. [4] (b) State the physical state of J at 25 °C. [1]

4. A student writes: “Water boils at 100 °C because that is the temperature at which the O–H bonds in the water molecules break.” Explain what is wrong with this statement. [3]

5. Use these values for ammonia, NH₃. Energy needed to boil 1 mol of liquid ammonia: 23 kJ. Energy needed to break one mole of N–H bonds: 391 kJ.

(a) Calculate the energy needed to break all the covalent bonds in 1 mol of ammonia molecules. [1] (b) Calculate how many times larger your answer to (a) is than the energy needed to boil 1 mol of ammonia. Give your answer to the nearest whole number. [1] (c) Explain what your answer to (b) shows about what happens when ammonia boils. [2]

6. This question is about metals.

(a) Explain why a copper wire conducts electricity. [2] (b) An iron pan heats up quickly all over when placed on a cooker. Explain, in terms of particles, why iron is a good conductor of heat. [2] (c) Molten lithium chloride and molten lithium metal both conduct electricity. Name the particles that carry the current in each. [2]

7. Sodium chloride is a white crystalline solid that melts at about 801 °C.

(a) Describe the structure of solid sodium chloride. [2] (b) Explain why sodium chloride has a high melting point. [3]

8. A student uses a battery, two electrodes and an ammeter to test five samples. Her results are shown.

Sample	Ammeter reading / A
Solid potassium iodide	0.00
Potassium iodide dissolved in water	0.35
Glucose dissolved in water	0.00
Strip of zinc	1.20
Liquid hexane	0.00

(a) Explain the difference between the two potassium iodide results. [2] (b) Glucose and hexane are both simple molecular substances. Explain why neither conducts. [1] (c) Explain why the zinc strip conducts. [1] (d) Suggest one variable the student should keep the same for every sample so that the readings can be compared fairly. [1]

9. An engineer has four materials. Use these values.

Material	Melting point / °C	Boiling point / °C	Conducts as solid?	Conducts when molten?
T	1455	2913	Yes	Yes
V	−13	197	No	No
W	1610	2230	No	No
X	714	1412	No	Yes

(a) Identify the type of structure of each material T, V, W and X. [4] (b) The engineer needs an electrically insulating container that stays solid while holding a molten salt at 900 °C. Choose the best material and explain your choice in terms of its structure and bonding. [2] (c) Choose the best material for electrical wiring. Explain your choice in terms of the particles in its structure. [2]

10. Use these values. Potassium chloride, KCl, melts at 770 °C. Chlorine, Cl₂, melts at −101 °C and boils at −34 °C.

(a) Use ideas about structure and bonding to explain why the melting point of potassium chloride is so much higher than that of chlorine. [4] (b) Explain why molten potassium chloride conducts electricity but liquid chlorine does not. [2] (c) State the physical state of chlorine at 25 °C. [1]

11. Use these values.

Substance	Melting point / °C	Boiling point / °C
P	−182	−162
Q	−78	−33
R	0	100
S	114	184

(a) Which substance or substances are gases at −50 °C? [1] (b) Which substance or substances are liquids at −50 °C? [1] (c) Which substance or substances are liquids at 120 °C? [1] (d) All four are simple molecular substances. Explain how their melting and boiling points support this. [1]

Answers

1. Lithium bromide is ionic; when molten, its ions are free to move [1]; the moving ions carry the charge, so it conducts [1]. [2] Examiner insight: An answer that says “electrons move” in a molten ionic compound usually scores nothing for the mechanism, so name the ions as the moving particles.

2. A: simple molecular (separate P₄ molecules) [1]. B: giant ionic (alternating oppositely charged ions) [1]. C: giant covalent (atoms joined by covalent bonds that continue in all directions) [1]. [3] Examiner insight: For C, the clue is the bonds running off the edges; a diagram of covalently bonded atoms is not automatically “molecular”.

3. (a) J: simple molecular (low melting and boiling points, no conduction) [1]. K: giant ionic (high melting point, conducts only when molten) [1]. L: metallic (conducts as a solid and when molten) [1]. M: giant covalent (very high melting point, never conducts) [1]. (b) 25 °C lies between −95 °C and 69 °C, so J is a liquid [1]. Examiner insight: Where a question asks you to identify from data, quoting the property that decides it (for K, conducting only when molten) makes the identification secure.

4. The O–H covalent bonds are not broken when water boils; the water molecules stay whole [1]. Boiling overcomes the intermolecular forces between water molecules [1]. These forces are weak compared with covalent bonds, which is why the boiling point is relatively low [1]. [3] Examiner insight: “The bonds are weak” is ambiguous; say which forces are weak (between molecules) and which are strong (covalent bonds within molecules).

5. (a) Each NH₃ molecule has three N–H bonds, so energy = 3 × 391 = 1173 kJ [1]. (b) 1173 ÷ 23 = 51 times [1]. (c) Boiling needs far less energy than breaking the covalent bonds, so the N–H bonds are not broken when ammonia boils [1]; only the weak intermolecular forces between ammonia molecules are overcome [1]. Examiner insight: In (a), forgetting that there are three bonds per molecule gives 391 kJ and carries the slip into (b), so count the bonds from the formula first.

6. (a) Copper contains delocalised electrons [1] that are free to move through the whole structure and carry charge [1]. (b) The delocalised electrons move freely through the metal [1] and carry energy quickly from the hot part to the rest of the pan [1]. (c) Molten lithium chloride: ions (Li⁺ and Cl⁻) [1]. Molten lithium: delocalised electrons [1]. Examiner insight: Part (c) is testing whether you can keep two mechanisms apart; writing “ions” for both, or “electrons” for both, loses a mark.

7. (a) A giant ionic lattice, a regular repeating arrangement of Na⁺ and Cl⁻ ions [1]; every ion has six nearest neighbours of opposite charge [1]. (b) There are strong electrostatic forces of attraction between the oppositely charged ions [1]; there are many of these forces, acting in all directions through the lattice [1]; overcoming them takes a lot of energy, so the melting point is high [1]. Examiner insight: The third mark in (b) depends on the energy link; “strong bonds so high melting point” leaves it out.

8. (a) In solid potassium iodide the ions are fixed in the lattice and cannot move [1]; when dissolved, the ions are free to move and carry the current [1]. (b) The molecules have no overall electric charge, so there are no charged particles to carry a current [1]. (c) Zinc is a metal with delocalised electrons that are free to move and carry charge [1]. (d) Any one of: the same battery voltage, the same distance between the electrodes, or the same depth the electrodes are dipped into the sample [1]. Examiner insight: In (d), “keep it fair” alone gains nothing; credit goes to a named variable that would actually change the reading.

9. (a) T: metallic [1]. V: simple molecular [1]. W: giant covalent [1]. X: giant ionic [1]. (b) W: it is giant covalent, with strong covalent bonds between all its atoms, so its melting point (1610 °C) is far above 900 °C [1]; it has no ions or delocalised electrons free to move, so it does not conduct [1]. (c) T: it is a metal, so it has delocalised electrons [1]; these drift through the metal when a voltage is applied, carrying the current [1]. Examiner insight: In (b), T and X are wrong for different reasons (T conducts; X would melt at 900 °C), so check every condition in the question against the data before choosing.

10. (a) Potassium chloride is a giant ionic lattice with strong electrostatic attractions between oppositely charged ions in all directions [1]; melting it means overcoming many of these strong forces, which needs a large amount of energy [1]. Chlorine is made of simple Cl₂ molecules [1]; melting it overcomes only the weak intermolecular forces between molecules, which needs little energy, and the Cl–Cl covalent bonds are not broken [1]. (b) In molten KCl the K⁺ and Cl⁻ ions are free to move and carry the current [1]; Cl₂ molecules have no overall charge, so liquid chlorine has no charged particles to carry a current [1]. (c) 25 °C is above −34 °C, so chlorine is a gas [1]. Examiner insight: A comparison needs a point about each substance; an answer that describes only potassium chloride cannot reach full marks in (a).

11. (a) P only (−50 °C is above its boiling point of −162 °C) [1]. (b) Q only (−78 < −50 < −33) [1]. (c) S only (114 < 120 < 184) [1]. (d) They all have relatively low melting and boiling points, showing that only weak intermolecular forces are overcome [1]. Examiner insight: Questions with negative temperatures are a common source of slips; writing the inequality, as in (b), shows your reasoning and catches errors.

Where marks are usually lost

• Stating that the covalent bonds inside molecules break on melting or boiling.
• Naming electrons as the charge carriers in molten or dissolved ionic compounds.
• Explaining a high melting point without saying that a large amount of energy is needed.
• Missing “oppositely charged” or “in all directions” when describing forces in an ionic lattice.
• Writing “strong intermolecular forces” for a giant covalent substance such as silicon dioxide.
• Answering only one side of a comparison question.
• Identifying a structure from data without quoting the property that decides it.
• Misordering negative temperatures when deciding states.

Next steps

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Official syllabus

Published by OxfordAQA: the International GCSE Chemistry (9202) specification, Version 6.2, valid for exams May/June 2018 onwards. This page follows its section 3.2.2, “How bonding and structure are related to the properties of substances”.