OCR A Level Chemistry A
OCR A Level Chemistry A Module 5: Physical Chemistry and Transition Elements Exam Questions
Free OCR A Level Chemistry A exam questions for Module 5: Physical Chemistry and Transition Elements, with a mark scheme for every pack. Covers rate equations, Arrhenius, Kc and Kp, pH and buffers, lattice enthalpy, entropy, free energy, electrode potentials and transition elements.
Module 5: Physical Chemistry and Transition Elements exam questions
3 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
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
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About OCR A Level Chemistry A Module 5: Physical Chemistry and Transition Elements
Module 5 of OCR A Level Chemistry A is the main physical chemistry module of the second year, plus transition elements. It covers rate equations, orders and half-lives, the Arrhenius equation, Kc and Kp, pH, Ka and buffers, then lattice enthalpy, entropy and free energy, redox and electrode potentials including redox titrations, and the properties and reactions of transition elements. In the A Level it is assessed in Paper 1 (Periodic table, elements and physical chemistry) and Paper 3 (Unified chemistry). Examiners set demanding calculations, graph analysis for orders and activation energy, and transition metal questions on complex ions, colour and precipitation reactions.
What you need to know
- 5.1.1 Rates Rate = k[A]^m[B]^n; orders from initial rates and concentration time graphs; for first order reactions half-life is constant and k = ln 2 / t1/2; rate-determining step; Arrhenius: ln k = -Ea/RT + ln A.
- 5.1.2 Equilibrium Kc and Kp, mole fractions and partial pressures; only temperature changes K; explaining shifts in position using K.
- 5.1.3 Acids, bases and buffers Bronsted-Lowry pairs; pH of strong acids, weak acids (Ka, pKa) and strong bases (Kw); buffer calculations and the carbonic acid-hydrogencarbonate buffer in blood; pH titration curves and indicators.
- 5.2.1 and 5.2.2 Enthalpy, entropy and free energy Born-Haber cycles, lattice enthalpy and the effect of ionic charge and radius; enthalpy of solution and hydration; entropy; delta G = delta H - T delta S and feasibility.
- 5.2.3 Redox and electrode potentials Manganate(VII) and iodine-thiosulfate titrations; standard electrode potentials, E cell and predicting feasibility; storage and fuel cells.
- 5.3 Transition elements Partly filled d subshells; complex ions, ligands, coordination number and shapes (including cis-trans and optical isomerism, cisplatin); ligand substitution; precipitation reactions with NaOH and NH3; redox reactions such as Fe2+ to Fe3+ and Cr2O7 2- to Cr3+.
Common mistakes in Module 5: Physical Chemistry and Transition Elements
- Using log instead of ln in the Arrhenius equation.
- Forgetting that the gradient of ln k against 1/T is -Ea/R, so Ea = -gradient x R.
- Leaving delta S in J K-1 mol-1 when delta H is in kJ mol-1.
- Writing the observed colour of a complex as the colour absorbed.
- Using hydrochloric acid in manganate(VII) titrations. Dilute sulfuric acid is used because chloride would be oxidised.
Try three Module 5: Physical Chemistry and Transition Elements exam-style questions
1. A first order reaction has a half-life of 30 s. Calculate the rate constant, k. (2 marks)
Show the mark scheme answer
k = ln 2 / t1/2 = 0.693 / 30; = 0.0231 s-1 (2.31 x 10^-2 s-1).
2. Calculate the pH of a buffer made with 0.200 mol dm-3 propanoic acid and 0.100 mol dm-3 sodium propanoate. Ka = 1.35 x 10^-5 mol dm-3. (2 marks)
Show the mark scheme answer
[H+] = Ka x [HA] / [A-] = 1.35 x 10^-5 x 0.200 / 0.100 = 2.70 x 10^-5 mol dm-3; pH = 4.57.
3. Explain why [Cu(H2O)6]2+ reacts with excess ammonia to give a deep blue solution, and write an equation. (3 marks)
Show the mark scheme answer
Ligand substitution: four water ligands are replaced by ammonia ligands; [Cu(H2O)6]2+ + 4NH3 gives [Cu(NH3)4(H2O)2]2+ + 4H2O; the new ligands change the d orbital splitting, so the colour changes to deep blue.
Module 5: Physical Chemistry and Transition Elements FAQs
What does OCR A Level Chemistry A Module 5: Physical Chemistry and Transition Elements cover?
It covers rate equations and the Arrhenius equation, Kc and Kp, pH and buffers, lattice enthalpy, entropy and free energy, redox titrations and electrode potentials, and transition element chemistry.
Which papers is Module 5 examined in?
In the A Level, Module 5 is assessed in Paper 1 (Periodic table, elements and physical chemistry) and Paper 3 (Unified chemistry).
What equations do I need for Module 5?
You need rate equations, k = ln 2 / t1/2, ln k = -Ea/RT + ln A, Kc and Kp, pH, Ka and Kw expressions, buffer [H+] = Ka[HA]/[A-], delta G = delta H - T delta S and E cell calculations.
