Units 3 and 4: Organic Chemistry, Equilibrium and Analysis
What you must understand
Units 3 and 4 extend the mole concept into organic chemistry, chemical equilibrium, acids and bases, redox and electrochemistry, and instrumental and volumetric analysis. You must be able to name and draw organic structures, predict reaction pathways, apply equilibrium and acid–base calculations, and evaluate analytical data.
Core concepts
- Organic chemistry: IUPAC naming, functional groups (alcohols, aldehydes, ketones, carboxylic acids, esters, amines, amides), isomerism, and reaction pathways such as oxidation, substitution, addition, condensation and hydrolysis.
- Equilibrium: Le Chatelier's principle, equilibrium constants K_c and K_a, ICE tables, and the relationship between K and reaction direction.
- Acids and bases: Brønsted–Lowry theory, pH, pOH, K_w, buffers, and titration curves.
- Redox and electrochemistry: oxidation numbers, half-equations, galvanic and electrolytic cells, and standard electrode potentials.
- Analysis: volumetric titrations, gravimetric analysis, chromatography, and spectroscopy (IR, NMR, mass spectrometry).
Traps
- Reversing oxidation and reduction definitions (oxidation is loss of electrons).
- Forgetting that pH = −log[H₃O⁺] applies to strong acids only without further calculation.
- Ignoring the effect of dilution on equilibrium position.
- Confusing empirical formula with molecular formula from mass spectra.
- Misreading titration equivalence points on curves.
Rule of thumb
Write balanced half-equations, then combine them so electrons cancel. For equilibrium, set up an ICE table before substituting into K expressions.
Worked example
Calculate the pH of 0.010 M HCl. HCl is a strong acid, so [H₃O⁺] = 0.010 M. pH = −log(0.010) = 2.00.