OCR A Level Chemistry A
OCR A Level Chemistry A Module 3: Periodic Table and Energy Exam Questions
Free OCR A Level Chemistry A exam questions for Module 3: Periodic Table and Energy, with a mark scheme for every pack. Covers periodicity, Group 2, the halogens, qualitative analysis, enthalpy changes, Hess's law, reaction rates and equilibrium including Kc.
Module 3: Periodic Table and Energy exam questions
5 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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A-Level Chemistry Flashcards for 2027 Onwards
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About OCR A Level Chemistry A Module 3: Periodic Table and Energy
Module 3 of OCR A Level Chemistry A combines inorganic chemistry of the periodic table with the physical chemistry of energy, rates and equilibrium. You study periodicity across Periods 2 and 3, ionisation energy trends, the reactions of Group 2 and the halogens, and qualitative tests for ions. The physical half covers enthalpy changes, calorimetry, Hess's law and bond enthalpies, reaction rates with the Boltzmann distribution and catalysts, and dynamic equilibrium with Kc. In the A Level it is assessed in the Periodic table, elements and physical chemistry paper and in Unified chemistry. Examiners favour explanations of trends, observations in tests, and calorimetry and Kc calculations.
What you need to know
- 3.1.1 Periodicity First ionisation energy increases across a period with small decreases at Groups 3 and 6; it decreases down a group. Melting points across Period 2 and 3 depend on giant metallic, giant covalent or simple molecular structure.
- 3.1.2 Group 2 Reactivity increases down the group as ionisation energies decrease. Group 2 metals react with water and oxygen; their hydroxides become more soluble and more alkaline down the group. Uses include Ca(OH)2 for treating acidic soil.
- 3.1.3 The halogens Boiling points increase down the group; oxidising power decreases. Displacement reactions show reactivity. Disproportionation of chlorine in water and cold dilute NaOH. Halide tests with silver nitrate and ammonia.
- 3.1.4 Qualitative analysis Test for carbonate (effervescence with acid), sulfate (white precipitate with Ba2+), halides (silver nitrate) and ammonium (ammonia gas with NaOH and warming), carried out in the order carbonate, sulfate, halide.
- 3.2.1 Enthalpy changes Definitions of standard enthalpy changes; calorimetry with q = mc delta T; Hess's law cycles; average bond enthalpies and why they differ from actual values.
- 3.2.2 and 3.2.3 Rates and equilibrium Collision theory, Boltzmann distribution, catalysts; dynamic equilibrium and le Chatelier's principle; Kc expressions and calculations for homogeneous equilibria.
Common mistakes in Module 3: Periodic Table and Energy
- Doing the qualitative tests in the wrong order, so that a carbonate gives a false positive with barium ions or a sulfate with silver nitrate.
- Forgetting that the Group 3 dip happens because the electron is in a p subshell of higher energy, not because of pairing.
- Leaving out the negative sign in exothermic calorimetry results.
- Saying the Boltzmann curve shifts to the left at higher temperature. The peak moves to the right and gets lower, with the same area underneath.
- Thinking Kc changes with concentration or pressure. Only temperature changes Kc.
Try three Module 3: Periodic Table and Energy exam-style questions
1. Use average bond enthalpies to calculate delta H for H2 + Cl2 gives 2HCl. Bond enthalpies (kJ mol-1): H to H 436, Cl to Cl 243, H to Cl 432. (2 marks)
Show the mark scheme answer
Bonds broken = 436 + 243 = 679; bonds formed = 2 x 432 = 864; delta H = 679 - 864 = -185 kJ mol-1.
2. A student tests a solution containing an unknown anion. Describe the sequence of tests to identify whether it contains carbonate, sulfate or chloride ions. (4 marks)
Show the mark scheme answer
Add dilute nitric acid: effervescence (gas turns limewater milky) shows carbonate; add barium nitrate: white precipitate shows sulfate; add silver nitrate: white precipitate soluble in dilute ammonia shows chloride; tests done in this order to avoid false positives.
3. Explain why the reactivity of Group 2 metals increases down the group. (3 marks)
Show the mark scheme answer
Atomic radius increases and there is more shielding; the outer electrons are less strongly attracted to the nucleus; so first and second ionisation energies decrease and the electrons are lost more easily.
Module 3: Periodic Table and Energy FAQs
What does OCR A Level Chemistry A Module 3: Periodic Table and Energy cover?
It covers periodicity, Group 2, the halogens, qualitative tests for ions, enthalpy changes and Hess's law, reaction rates with the Boltzmann distribution and catalysts, and equilibrium including Kc.
Which papers is Module 3 examined in?
In the A Level, Module 3 is assessed in Paper 1 (Periodic table, elements and physical chemistry) and Paper 3 (Unified chemistry).
What practical skills does Module 3 involve?
Expect questions on calorimetry and its errors, measuring rates (gas collection, mass loss), carrying out qualitative tests in the correct order and interpreting observations.
