Edexcel IAL Chemistry Unit 5 — Transition Metals and Organic Nitrogen Chemistry

Seventeen WCH15 papers from 2020 to 2026 — 831 parts, 1,530 marks. Transition metals and their chemistry is the biggest topic at 31%, then organic synthesis and analysis at 23% and redox equilibria at 19%. Organic nitrogen compounds are 16% and arenes 11%. Transition metals plus synthesis is more than half the paper.

Multiple choice ("Which", "What") is a third of question parts. Then "Explain" 10%, "Calculate" 7% — mainly E°cell, redox titrations and percentage yields — and "Draw" 5%, which in Unit 5 means mechanisms for electrophilic substitution and complex-ion shapes. Twenty-eight percent of parts are high-difficulty, the highest of the three A2 papers: the extended synthesis routes and the unfamiliar context in Section C. Learn the transition-metal reactions as a table of observations and equations first; that topic alone is nearly a third of the marks.

Standard electrode potentials and the hydrogen electrode, cell diagrams, E°cell from two half-cells and what it predicts — thermodynamic feasibility, its link to ΔS_total and ln K, and why a feasible reaction may still not happen. Disproportionation predicted from E° values. Then the two titrations that appear every year: Fe²⁺ with manganate(VII) and thiosulfate with iodine, structured and unstructured, with uncertainty discussion. Fuel cells finish the topic. Core Practicals 12 (electrochemical cells) and 13a/13b (redox titrations) are examined here and in Unit 6.

Definition, electronic configurations Sc to Zn, variable oxidation number, ligands and dative bonding, coordination number and shape — octahedral with water, hydroxide and ammonia, tetrahedral with chloride, square planar cis-platin. Colour from d-orbital splitting and why some ions are colourless. Vanadium's four oxidation-state colours and dichromate/chromate chemistry. The reactions of Cr³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ with sodium hydroxide and ammonia, including excess, and the ligand exchanges with EDTA and chloride. Heterogeneous and homogeneous catalysis, including autocatalysis. Core Practical 14 prepares a transition-metal complex.

Evidence for benzene's delocalised structure — bond lengths, hydrogenation enthalpies, reactivity. Electrophilic substitution: nitration, halogenation with a halogen carrier, Friedel–Crafts alkylation and acylation, each with mechanism and the generation of the electrophile. Phenol: why it is more reactive than benzene, and its reactions with bromine water, sodium hydroxide and sodium.

Amines: preparation from halogenoalkanes, nitriles and nitrobenzene; basicity and why aromatic amines are weaker; reactions with acids, acyl chlorides, halogenoalkanes and copper(II) ions. Diazotisation and azo dyes. Amides and their hydrolysis. Amino acids, zwitterions and isoelectric point; peptides and proteins; condensation polymers — polyamides and polyesters. Core Practical 15 identifies inorganic and organic unknowns.

The techniques: reflux, distillation, solvent extraction, recrystallisation, melting temperature as a purity check, TLC. Then the reagents, conditions and mechanisms for every reaction in the specification, assembled into synthetic routes of up to four steps, including Grignard reagents and chain-lengthening through nitriles. Percentage yield and atom economy for each route. Core Practical 16 prepares aspirin.