OCR GCSE Chemistry A: The particle model (J248) – 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.

Covered here: sub-topic C1.1 The particle model in OCR GCSE (9–1) Chemistry A (Gateway Science), following the J248 specification (Version 4.0, August 2026): learning outcomes C1.1a to C1.1c, the maths outcome CM1.1i and the practical suggestion. C1.1c is Higher Tier only, so questions 9 and 10 are labelled. Everything else suits both tiers. Topic C1 is examined in Paper 1 at Foundation Tier and Paper 3 at Higher Tier.

Learn the content first from the particle model study guide. Course pages: OCR GCSE Chemistry and the J248 topic checklist.

Questions

1. Name the change of state in each example.

(a) A puddle dries on a warm pavement. [1] (b) Dew forms on grass on a cool morning. [1] (c) Solder turns runny when touched by a hot soldering iron. [1] (d) Molten glass sets hard as it cools. [1]

2. A steel cylinder can hold a large mass of oxygen squeezed into a small volume. A bottle already full of water cannot have more water forced in. Explain this difference in terms of particles. [3]

3. Use the data in this table.

Substance	Melting point / °C	Boiling point / °C
J	−98	65
K	80	218
L	−188	−42
M	660	2519

(a) Which substance is a liquid at 25 °C? [1] (b) Which substance is a gas at 25 °C? [1] (c) The substances are warmed from 25 °C to 100 °C. Name the two substances that change state, and name each change. [2]

4. For each change, state whether it is physical or chemical, and explain your answer in terms of particles.

(a) A piece of gallium metal melts when held in a warm hand. [2] (b) A copper roof slowly turns green over many years as the copper forms a new compound. [2] (c) The alcohol in hand gel evaporates from your skin. [2]

5. Liquid ethanol is heated from 20 °C until it boils at 78 °C. Describe what happens to the ethanol particles during this process. [4]

6. Two students make these statements.

Student 1: “A metal rail gets longer on a hot day because its particles get bigger.” Student 2: “Between the particles of a gas there is air.”

Explain what is wrong with each statement. [4]

7. A student sets up two test tubes.

Tube	What the student does	Observations
A	Warms a white waxy solid in a beaker of hot water	Solid turns to a clear liquid
B	Adds a piece of magnesium ribbon to dilute hydrochloric acid	Bubbles form, the ribbon gets smaller and disappears, the tube feels warm

(a) State which tube shows a chemical change. Give two observations that support your answer. [3] (b) Describe what happens to the particles in tube B. [2] (c) Suggest how the student could show that the change in tube A is physical. [1]

8. A model of a solid is built as a cube of polystyrene balls, 6 balls along each edge.

(a) Calculate the total number of balls. [1] (b) State how many balls a 2D drawing of one face would show. [1] (c) Calculate how many balls are completely hidden inside the cube. [1] (d) Give one way in which a 2D diagram of a solid gives a misleading picture of its structure. [1]

9. (Higher Tier only) Use these values. 1.0 g of liquid X occupies 1.25 cm³. As a gas, at the conditions used, 1.0 g of X occupies 1000 cm³. A textbook diagram of gaseous X draws each particle as a circle 3 mm across, with centres about 6 mm apart.

(a) Calculate how many times larger the volume of the gas is than the volume of the liquid. [1] (b) Estimate how many times further apart the particles are in the gas than in the liquid. [2] (c) Use your answer to (b) to comment on the textbook diagram. [2] (d) Give two other limitations of drawing particles as inelastic spheres. [2]

10. (Higher Tier only) Substance N melts at −114 °C; substance Z melts at 1085 °C. A student explains melting with a model in which every particle is a hard, identical ball. Explain why this model cannot account for the difference in melting points, and state the idea that is needed. [4]

11. A small amount of white ammonium chloride is heated at the bottom of a test tube. The solid at the bottom disappears, and a white solid collects on the cooler part of the tube near its mouth. Tests show that the gas in the hot part of the tube is a mixture of ammonia and hydrogen chloride.

(a) Write a word equation for the change at the bottom of the tube. [1] (b) Student A says: “This is sublimation, so it is a physical change.” Student B says: “Two chemical changes happen.” Evaluate the two claims, using the particle model. [5] (c) Explain what this example shows about using reversibility to decide whether a change is chemical. [1]

12. Smoke in a small glass cell is viewed under a microscope. The bright specks move in a jerky, random way, though the air is still. Explain how this observation supports the particle model. [3]

Answers

1. (a) Evaporation [1]. (b) Condensation [1]. (c) Melting [1]. (d) Freezing (solidifying) [1]. Examiner insight: Use the scientific name of the change; everyday words such as “drying” or “setting” repeat the question rather than answer it.

2. Gas particles are far apart with empty space between them [1]. Squeezing the gas pushes the particles closer together into that space, so a large mass fits in a small volume [1]. Water particles are already close together and touching, so there is almost no space to push them into [1]. [3] Examiner insight: Describe the liquid particles too, not only the gas.

3. (a) J (25 °C is between −98 °C and 65 °C). [1] (b) L (25 °C is above −42 °C). [1] (c) K melts (passes 80 °C) [1]; J boils (passes 65 °C) [1]. Examiner insight: Name the change as well as the substance; “J changes” is incomplete.

4. (a) Physical [1]. The gallium particles gain energy and start to move past each other, but they are still gallium particles; no new substance forms [1]. (b) Chemical [1]. Copper atoms are rearranged with atoms from the air to make new particles of a different substance (the green compound) [1]. (c) Physical [1]. The alcohol particles gain energy and spread out as a gas, but they are the same alcohol particles; no new substance forms [1]. Examiner insight: “It can be reversed” is not a particle explanation; say whether the particles stay the same or new ones form.

5. The particles take in energy [1]. They move faster [1]. At 78 °C they move far apart as a gas, moving quickly and randomly [1]. The particles stay the same: still ethanol molecules, no bigger [1]. [4] Examiner insight: A description that covers energy, movement and spacing gains more credit than one that only says “the particles move faster”.

6. Student 1: the particles do not get bigger [1]. They gain energy and vibrate more, so they take up more room and the rail as a whole expands [1]. Student 2: the space between gas particles is empty [1]. Air is itself made of particles, so there cannot be air between them [1]. [4] Examiner insight: For an “explain what is wrong” question, state the correct idea as well as saying the statement is wrong.

7. (a) Tube B [1]. Bubbles show a gas is made [1]. The magnesium disappears, so it has been used up to make something new (or: the tube warms up, so energy is given out) [1]. [3] (b) The atoms in the magnesium and in the acid are rearranged [1] to make new particles: hydrogen molecules and magnesium chloride, which are new substances [1]. [2] (c) Let it cool: it sets back into the same white solid, which melts again at the same temperature [1]. [1] Examiner insight: Quote observations from the table, not general signs of reaction.

8. (a) 6 × 6 × 6 = 216 [1]. (b) 6 × 6 = 36 [1]. (c) Inner cube is 4 balls along each edge: 4 × 4 × 4 = 64 [1]. (d) It shows only one layer, hiding the particles behind and inside (or: it makes a 3D arrangement look flat) [1]. Examiner insight: Show the multiplication; a bare wrong number shows no method.

9. (a) 1000 ÷ 1.25 = 800 [1]. (b) Spacing increases by the cube root of the volume ratio [1]: ∛800 ≈ 9.3, so about 9 times further apart [1]. (c) To scale, the centres should be about 9.3 × 3 mm ≈ 28 mm apart, not 6 mm [1]. The diagram shows the particles far too close; the real spaces are much larger [1]. (d) It ignores the forces of attraction between particles [1]. It shows all particles as the same size, when real particles differ in size (or: real particles are not hard, solid balls) [1]. [2] Examiner insight: The spacing comes from the cube root; dividing by 3 or using 800 directly loses the method.

10. The model shows no forces of attraction between the particles [1]. Melting needs energy to overcome the attractions holding the particles in place [1]. Z must have much stronger forces between its particles than N, so needs much more energy [1]. The idea needed is that particles, and the forces between them, differ from one substance to another [1]. [4] Examiner insight: Name the missing idea (forces of attraction) explicitly; “the model is too simple” does not say what is missing.

11. (a) ammonium chloride → ammonia + hydrogen chloride [1]. (b) Student A is wrong [1]. In sublimation the same particles would just move apart as a gas [1]. Here the gas is ammonia and hydrogen chloride, different substances, so atoms have been rearranged into new particles [1]. Student B is right: the ammonium chloride breaks down into new substances at the bottom of the tube [1], and at the cool end ammonia and hydrogen chloride particles react to form new ammonium chloride particles, which is a second chemical change [1]. [5] (c) It shows that a chemical change can be reversed, so reversibility alone does not show a change is physical; the test is whether new substances form [1]. Examiner insight: Judge each claim and back it with evidence from the question, here the identity of the gases.

12. The smoke specks are hit by air particles that are too small to see [1]. The air particles move fast and in random directions [1]. The specks are hit unevenly from different sides at different moments, so they are pushed in a jerky, random path, which is evidence that tiny moving particles exist [1]. [3] Examiner insight: Say that invisible air particles do the hitting; “the smoke vibrates” explains nothing.

Where marks are usually lost

• Saying particles get bigger, melt or get hot, instead of gaining energy and moving faster.
• Describing only one of arrangement, movement and spacing.
• Reading negative melting and boiling points the wrong way round.
• Classifying a change as physical or chemical with no reference to new particles or new substances.
• (Higher Tier only) Using a volume ratio directly as a spacing ratio instead of taking the cube root.
• (Higher Tier only) Writing “the model is too simple” without naming forces, sizes or spaces.

Next steps

• Revise with the revision notes
• Re-read the particle model study guide
• Go on to atomic structure, C1.2
• Book a free trial class
• Take any of our free 10-minute diagnostics
• OCR GCSE Chemistry hub page
• J248 printable checklist

Official syllabus

J248 is the code for OCR GCSE (9–1) Chemistry A (Gateway Science); this page follows its specification, Version 4.0 (August 2026), for first assessment in 2018 (publisher: OCR); unit C1.1 The particle model.