WCH15 Transition Metals and Organic Nitrogen Chemistry

Lessons in WCH15

1. Standard electrode potentials and the hydrogen electrode
   E° is measured against the standard hydrogen electrode (0.00 V) at 298 K, 100 kPa and 1.00 mol dm^-3. Use Pt for ion/ion or gas/ion half-cells; a KNO3 salt brid
2. Cell emf, cell diagrams and fuel cells (Core Practical 12)
   E°cell = E°(positive) - E°(negative). Cell diagram: oxidation half-cell on the left, || for the salt bridge. E changes with concentration and temperature. H2/O2
3. Predicting redox reactions, limitations and disproportionation
   Feasible if E°cell is positive. E°cell is proportional to ΔStotal and ln K. Limitations: rate (high Ea) and non-standard conditions. Disproportionation: one spe
4. Redox titrations with manganate(VII) (Core Practical 13a)
   MnO4- : Fe2+ = 1 : 5; MnO4- : C2O4²- = 2 : 5. Acidify with dilute H2SO4. End point: first permanent pale pink. Titre uncertainty ±0.10 cm³.
5. Iodine-thiosulfate titrations (Core Practical 13b)
   I2 : S2O3²- = 1 : 2. Cu2+ : S2O3²- = 1 : 1 (2Cu2+ + 4I- -> 2CuI + I2). IO3- : S2O3²- = 1 : 6. Add starch near the end point; blue-black to colourless.
6. Transition metals: electron configurations and oxidation states
   Transition metal: forms a stable ion with a partly filled d sub-shell (so not Sc or Zn). Lose 4s before 3d. Variable oxidation states because 3d and 4s energies
7. Ligands, complex ions and their shapes
   Ligand: lone-pair donor forming a dative bond to the metal ion. Coordination number = number of dative bonds. Small ligands: octahedral (6). Cl-: tetrahedral (4
8. Why transition metal complexes are coloured
   Ligands split d orbitals; electrons absorb visible light of energy ΔE = hf; we see the complementary colour. d0 and d10 ions are colourless. Oxidation number, l
9. Bidentate and hexadentate ligands, chelates and haemoglobin
   Bidentate (en, ethanedioate): 2 bonds; hexadentate (EDTA4-): 6 bonds. Swapping monodentate for polydentate ligands increases the number of particles, so ΔSsyste
10. Redox chemistry of vanadium and chromium
    Vanadium: +5 yellow, +4 blue, +3 green, +2 violet; zinc/acid reduces all the way. Chromium: Zn/acid gives Cr3+ (green) then Cr2+ (blue); H2O2 in alkali oxidises
11. Reactions of aqueous ions with hydroxide and ammonia
    OH- deprotonates water ligands, precipitating hydroxides. Cr(OH)3 and Zn(OH)2 are amphoteric. Excess NH3 dissolves Cr, Co, Ni, Cu and Zn hydroxides by ligand ex
12. Ligand exchange and preparing a complex (Core Practical 14)
    NH3 with Cu2+: deep blue [Cu(NH3)4(H2O)2]2+, still 6-coordinate. Conc HCl: [CuCl4]2- yellow and [CoCl4]2- blue, tetrahedral. CP14: prepare a complex, crystallis
13. Transition metals as catalysts
    Heterogeneous: different phase, works at a surface (V2O5 by changing oxidation number; converters by adsorption and desorption). Homogeneous: same phase, via an
14. The structure and stability of benzene
    Benzene is more stable than Kekulé predicts (hydrogenation -208 not -360 kJ mol^-1), all C-C bonds are 0.139 nm, and p orbitals overlap into a delocalised π rin
15. Electrophilic substitution: halogenation, nitration and sulfonation
    Electrophilic substitution: ring attacks E+, intermediate cation, H+ lost. Br2/FeBr3 gives Br+; conc HNO3 + conc H2SO4 at 50 °C give NO2+; fuming H2SO4 sulfonat
16. Friedel-Crafts reactions and phenol
    Alkylation: RCl + AlCl3 gives R+; acylation: RCOCl + AlCl3 gives RCO+ (aromatic ketone). Dry conditions. Phenol decolourises bromine water at room temperature,
17. Amines: basicity and reactions
    Amine lone pair: base, nucleophile, ligand. Strength: aliphatic amine > NH3 > aromatic amine. Reactions: water (alkaline), acids (salts), halogenoalkanes (furth
18. Making amines and azo dyes
    Halogenoalkane + excess ethanolic NH3 (sealed tube), or nitrile + LiAlH4, gives primary amines. Nitrobenzene + Sn/conc HCl, then NaOH, gives phenylamine. NaNO2/
19. Amides and polymers
    Acyl chloride + NH3 or amine gives amides. Condensation polymers: polyesters (diol + diacid), polyamides (diamine + diacid or diacyl dichloride), proteins. Poly
20. Amino acids, peptides and proteins
    Amino acids H2NCH(R)COOH: zwitterions +H3NCH(R)COO-, high melting points. Chiral except glycine. Peptide link -CONH- forms by condensation; acid hydrolysis brea
21. Identifying organic compounds (Core Practical 15)
    Combustion: C from CO2 (x 12/44), H from H2O (x 2/18), O by difference. Tests identify groups; spectra confirm structure. CP15: systematic tests on inorganic an
22. Grignard reagents and lengthening carbon chains
    RX + Mg in dry ether gives RMgX. With CO2: carboxylic acid; methanal: primary alcohol; other aldehydes: secondary; ketones: tertiary; then dilute acid. Keep eve
23. Planning multi-step syntheses
    Count carbons and compare functional groups; add carbon with CN-, HCN, Grignard or Friedel-Crafts. Give reagent, conditions and intermediate for each step. Choo
24. Practical techniques and preparing aspirin (Core Practical 16)
    Reflux, distil (or steam distil), extract, wash, dry. Recrystallise: minimum hot solvent, hot filter, cool, filter under reduced pressure, wash with cold solven

Next exams for WCH15

• January 2027: Thu 21 Jan 2027, morning, 1h 45m
• Summer 2027: Wed 2 Jun 2027, morning, 1h 45m

From Pearson's final timetables. All exam dates. Always confirm your entries with your exams officer.