Edexcel A-Level Chemistry Paper 2, June 2023: Question 2

✅ Correct Answer

B — a biofuel and renewable

💡 Key Knowledge

Fuels derived from biomass (plants/crops) are classified as biofuels. Because crops can be regrown continually over a short time frame, the fuel is considered renewable.

❌ Common Errors

Choosing option A or C. Students sometimes confuse fermentation products with fossil fuels, or forget that plant-derived fuels are naturally renewable.

✅ Correct Answer

CH₃OH + 1.5O₂ → CO₂ + 2H₂O

(Or multiplied across by 2 to use whole numbers: 2CH₃OH + 3O₂ → 2CO₂ + 4H₂O )

🧠 Exam Technique

Always balance carbon first, hydrogen second, and leave oxygen (especially O₂) until the very end. Fractions like 1.5 or 3/2 are fully accepted by Edexcel.

❌ Common Errors

Forgetting to include oxygen as a reactant, or producing carbon monoxide ( CO ) or carbon ( C ) instead of carbon dioxide ( CO₂ ), which violates the "complete combustion" requirement.

✅ Correct Answer

Red phosphorus and iodine ( P + I₂ or P₄ + 6I₂ ) OR phosphorus(III) iodide ( PI₃ ).

💡 Key Knowledge

To substitute a hydroxyl group ( -OH ) with an iodine atom, we generate hydrogen iodide in situ using red phosphorus and iodine. Alternatively, pre-formed PI₃ can be used.

❌ Common Errors

Using potassium iodide and sulfuric acid ( KI + H₂SO₄ ). Sulfuric acid oxidises hydrogen iodide to iodine gas, preventing the formation of the desired 1-iodopropane. Also, do not confuse phosphorus(III) iodide ( PI₃ ) with phosphorus(V) iodide ( PI₅ , which does not exist stably).

✅ Correct Answer

B — 1485 – 1365 , 2962 – 2853 and 3750 – 3200 cm⁻¹

💡 Key Knowledge

Propan-2-ol contains an -OH alcohol group (broad peak at 3750 – 3200 cm⁻¹ ), C-H saturated alkane stretches ( 2962 – 2853 cm⁻¹ ), and C-H bending/fingerprint signals ( 1485 – 1365 cm⁻¹ ).

❌ Common Errors

Selecting wavenumber ranges associated with carboxylic acid -OH ( 3300 – 2500 cm⁻¹ ), which appears much broader and extends further down into lower wavenumbers.

✅ Correct Answer

2 / two peaks

💡 Key Knowledge

Propan-2-ol ( CH₃CH(OH)CH₃ ) possesses a plane of symmetry through the central carbon and oxygen atom. Therefore, the two terminal methyl groups are chemically equivalent (1 environment), and the central carbon bonded to the -OH group forms the second unique carbon environment.

❌ Common Errors

Writing 3 peaks by counting every individual carbon atom without accounting for molecular symmetry.

✅ Correct Answer

CH₃CH₂OH + H₂O → CH₃COOH + 4H⁺ + 4e⁻

(Accepting valid multiples or electrons on the left as -4e⁻ )

🧠 Exam Technique

Construct half-equations methodically: balance the main organic carbon skeleton first, balance oxygen using water ( H₂O ), balance hydrogen using hydrogen ions ( H⁺ ), and finally balance overall charge using electrons ( e⁻ ).

❌ Common Errors

Failing to balance oxygen atoms correctly (forgetting the H₂O on the reactant side), or getting the electron count wrong due to miscalculating the change in oxidation state of carbon.