OCR GCSE Chemistry A: Predicting chemical reactions (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.

Every question below is on sub-topic C4.1 Predicting chemical reactions of the OCR GCSE (9–1) Chemistry A (Gateway Science) J248 specification (Version 4.0, August 2026). They test learning outcomes C4.1a–C4.1f, CM4.1i and the linked PAG C1, C5, C7 and C8 practicals. As C4.1 contains no Higher-Tier-only statements, Foundation and Higher candidates can attempt every question. Topic C4 is examined on Paper 2 (Foundation Tier) and Paper 4 (Higher Tier).

Revise first with the study guide or revision notes.

Questions

1. Densities of Group 0 gases under the same conditions: helium 0.18 g/dm³, neon 0.90 g/dm³, argon 1.78 g/dm³, krypton 3.75 g/dm³, xenon 5.89 g/dm³.

(a) Explain, in terms of electrons, why the noble gases are very unreactive. [2] (b) Radon is the next element down Group 0. Predict its density under the same conditions. [1]

2. Rubidium is directly below potassium in Group 1. Atomic radii: lithium 0.152 nm, sodium 0.186 nm, potassium 0.227 nm.

(a) Predict the atomic radius of rubidium. [1] (b) A tiny piece of rubidium is dropped into water behind a safety screen. Describe two expected observations. [2] (c) Give the balanced symbol equation when rubidium reacts with water. [2] (d) Explain why rubidium is more reactive than potassium. [3]

3. In a PAG C1 practical, a student adds each halogen solution to the other two potassium halide solutions. Chlorine water turns potassium bromide orange and potassium iodide brown. Bromine water turns potassium iodide brown. The other three mixtures show no colour change.

(a) Identify the mixtures that reacted, and use them to rank the three halogens by reactivity. [2] (b) Give the word equation and the balanced symbol equation when chlorine reacts with potassium iodide. [2] (c) Explain, in terms of electrons, why chlorine is more reactive than iodine. [3] (d) Predict whether iodine would react with a solution of potassium astatide. Give a reason. [1]

4. A student heats 2.60 g of chromium in chlorine. The product, a chromium chloride, has a mass of 6.15 g. (Ar: Cr = 52, Cl = 35.5)

(a) Calculate the empirical formula of the chromium chloride. [3] (b) State the charge on the chromium ion in this compound. [1] (c) Chromium also forms a chloride with the formula CrCl₃. State which property of transition metals this shows. [1]

5. A student adds equal-sized pieces of four metals to separate 50 cm³ portions of the same dilute hydrochloric acid and collects the hydrogen for 60 s.

Metal	Volume of hydrogen in 60 s (cm³)
magnesium	54
zinc	18
iron	6
copper	0

(a) Calculate the mean rate of hydrogen production for magnesium. Give the unit. [2] (b) Put the four metals in order of reactivity, most reactive first. [1] (c) Explain the order in terms of the metal ions formed. [2] (d) State two variables, other than the acid’s volume, that must be kept the same. [2] (e) Give the balanced symbol equation when zinc reacts with hydrochloric acid. [2]

6. Equal masses of five metal powders are added in turn to 30 cm³ portions of copper(II) sulfate solution in a polystyrene cup. The starting temperature is 19.5 °C each time.

Metal	magnesium	zinc	iron	nickel	silver
Highest temperature (°C)	44.0	27.5	23.0	21.5	19.5

(a) Calculate the temperature rise for each metal. [2] (b) Use the results to place all six metals, including copper, in order of reactivity. [2] (c) Explain the result for silver. [1]

7. Element G is in Group 2 and Period 4 of the Periodic Table. Element J is in Group 6 and Period 3.

(a) State whether each element is a metal or a non-metal. [1] (b) Predict whether the oxide of J is acidic or basic, and the pH range of its solution in water. [2] (c) G forms G²⁺ ions and J forms J²⁻ ions. Predict the formula of the compound formed between G and J. [1] (d) Predict whether G or the Group 2 element directly above it reacts more vigorously with water. [1]

8. A student heats 5.08 g of copper powder in air until there is no further change. The black product has a mass of 6.36 g. A second 5.08 g sample is heated with a limited supply of air and forms 5.72 g of a red oxide. (Ar: Cu = 63.5, O = 16)

(a) Explain why the product is heavier than the copper. [1] (b) Calculate the empirical formula of the black oxide. [3] (c) Calculate the empirical formula of the red oxide. [2] (d) State the charge on the copper ion in each oxide. [1]

9. Three halogens as found at room temperature: chlorine, a pale green gas; bromine, a red-brown liquid; iodine, a grey-black solid. Fluorine is above chlorine in Group 7.

(a) Predict the state of fluorine at room temperature, and whether its colour is paler or darker than that of chlorine. [2] (b) Explain why the states change from gas to solid down Group 7. [2] (c) Hydrogen bromide gas is dissolved in water. Predict whether the solution is acidic or alkaline. [1] (d) Hot iron wool reacts vigorously with chlorine. Predict how its reaction with iodine vapour compares, and give a reason. [1]

10. A metal M has these properties:

• no reaction with cold water, but slow bubbling in dilute hydrochloric acid
• displaces copper from copper(II) sulfate solution, but does not displace zinc from zinc sulfate solution
• forms a pale green chloride, MCl₂, and an orange-brown chloride, MCl₃

(a) Identify metal M. Use three pieces of evidence to support your answer. [4] (b) M reacts with copper(II) sulfate solution to form MSO₄. Give the balanced symbol equation. [1] (c) Suggest one industrial use of M as a catalyst. [1]

Answers

1. (a) Each atom has a full outer shell of electrons [1], which is stable, so atoms do not lose, gain or share electrons [1]. (b) Any value from 8 to 11 g/dm³ [1] (the gaps between neighbours keep increasing). Examiner insight: “Full outer shell” is only half an explanation; link it to the atoms not losing, gaining or sharing electrons.

2. (a) Any value from 0.235 nm to 0.290 nm [1]. (b) Any two: melts; fizzes very rapidly; ignites or explodes; disappears quickly [1] [1]. (c) Formulae correct, RbOH and H₂ [1]; balanced: 2Rb + 2H₂O → 2RbOH + H₂ [1]. (d) Rubidium has one more occupied shell, so its single outer electron sits further out [1]; extra inner shells shield it, weakening the pull of the nucleus [1]; so rubidium loses that electron more readily [1]. Examiner insight: For (d), “it has more shells” is only a start; the answer needs weaker attraction and easier electron loss to be complete.

3. (a) Reactions: chlorine + bromide, chlorine + iodide, bromine + iodide [1]. Order: chlorine > bromine > iodine [1]. (b) chlorine + potassium iodide → potassium chloride + iodine [1]; Cl₂ + 2KI → 2KCl + I₂ [1]. (c) Halogens react by gaining one electron [1]. A chlorine atom is smaller, with fewer inner shells shielding its nucleus [1], so the nucleus pulls an incoming electron in more strongly and chlorine forms its ion more readily [1]. (d) Yes: iodine is above astatine, so it is more reactive and displaces it [1]. Examiner insight: An argument about electrons being lost more easily is unlikely to gain credit for a halogen, because halogens gain electrons.

4. (a) Cl = 6.15 − 2.60 = 3.55 g [1]. Cr: 2.60 ÷ 52 = 0.050 mol; Cl: 3.55 ÷ 35.5 = 0.100 mol [1]. Ratio 1 : 2, so CrCl₂ [1]. (b) 2+ [1] (c) Transition metals form ions with different charges [1]. Examiner insight: Show the chlorine mass and both mole values, not just the formula.

5. (a) 54 ÷ 60 = 0.90 [1]; 0.90 cm³/s [1]. (b) magnesium > zinc > iron > copper [1] (c) The more reactive metal loses electrons to form its positive ion more easily [1]; copper does not form ions with dilute acid, so no hydrogen is made [1]. (d) Any two: concentration of acid; temperature; size, mass or surface area of the metal [1] [1]. (e) ZnCl₂ and H₂ as products [1]; Zn + 2HCl → ZnCl₂ + H₂ [1]. Examiner insight: A rate without its unit is incomplete; cm³/s must be stated.

6. (a) Mg 24.5 °C, Zn 8.0 °C [1]; Fe 3.5 °C, Ni 2.0 °C, Ag 0.0 °C [1]. (b) Magnesium > zinc > iron > nickel from the size of the rises [1]; copper below nickel and above silver [1]: magnesium > zinc > iron > nickel > copper > silver. (c) Silver is less reactive than copper, so it cannot displace it and no energy is released [1]. Examiner insight: Ranking by final temperature works only because the start temperature was fixed; showing the subtraction makes the method clear.

7. (a) G is a metal; J is a non-metal [1]. (b) Acidic [1]; pH below 7 [1]. (c) GJ [1] (charges 2+ and 2− balance one to one). (d) G reacts more vigorously, because reactivity of metals increases down a group [1]. Examiner insight: For (c), write the simplest ratio that balances the charges; G₂J₂ balances but is not the simplest formula.

8. (a) Oxygen from the air has combined with the copper [1]. (b) O = 6.36 − 5.08 = 1.28 g [1]. Cu: 5.08 ÷ 63.5 = 0.080 mol; O: 1.28 ÷ 16 = 0.080 mol [1]. Ratio 1 : 1, so CuO [1]. (c) O = 0.64 g = 0.040 mol; Cu = 0.080 mol [1]. Ratio 2 : 1, so Cu₂O [1]. (d) Cu²⁺ in CuO and Cu⁺ in Cu₂O [1]. Examiner insight: Dividing each mass by its Ar before finding the ratio is the step that matters; a ratio of masses gives the wrong formula.

9. (a) Gas [1]; paler (fluorine is pale yellow) [1]. (b) Halogen molecules are bigger lower in the group [1]; attractions between neighbouring molecules rise, so higher temperatures are needed to melt and boil them [1]. (c) Acidic [1]. (d) Less vigorous, because iodine is less reactive than chlorine [1]. Examiner insight: In (b) the forces that matter act between molecules; an answer about breaking the covalent bond inside each molecule is unlikely to be credited.

10. (a) M is iron [1]. Evidence (any three): slow with acid, none with cold water, so moderately reactive [1]; displaces copper but not zinc, so lies between them [1]; two coloured chlorides, so coloured ions with different charges, typical of a transition metal [1]. (b) Fe + CuSO₄ → FeSO₄ + Cu [1] (c) Catalyst in the Haber process for making ammonia [1]. Examiner insight: Give each observation with what it shows; a bare list of observations gains little.

Where marks are usually lost

• Using the Group 1 explanation for Group 7, or saying halogens get more reactive down the group.
• Writing “it wants a full shell” instead of describing attraction between the nucleus and the outer electron.
• Writing chlorine as Cl, or forgetting to double the potassium halide in a displacement equation.
• Giving a single fixed charge for a transition metal.
• Dividing masses instead of moles when finding an empirical formula.
• Saying the metal lost mass when it formed an oxide or chloride.

Next steps

• Recap with the revision notes.
• Re-read the study guide for anything you found hard.
• Browse the OCR GCSE Chemistry hub and tick off C4.1 on the J248 checklist.
• Try one of the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OCR GCSE (9–1) Chemistry A (Gateway Science) J248 specification, Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Sub-topic C4.1 Predicting chemical reactions, learning outcomes C4.1a–C4.1f, mathematical learning outcome CM4.1i and the linked practical suggestions (PAG C1, C5, C7, C8).