Chemistry
Carboxylic Acids
2,927 words, 11 sections. The first two are free.
The opening sections
Definitions first, then the reasoning. Each section is short enough to read in one sitting.
The carboxyl group, , sits where the chemistry of the carbonyl and the hydroxyl meet, and the paper treats it as one large chapter rather than a set of unrelated reactions. It has 175 distinct questions across 78 official papers between 2000 and 2026, and it carries a share of the 45 Chemistry marks in the paper. A student who has mastered it can name any acid, derivative and ester, rank a series of acids by strength without calculating anything, and predict the product when an acid meets a base, a carbonate, a metal, an alcohol, ammonia, thionyl chloride or lithium aluminium hydride.
The carboxyl carbon is hybridised, with three orbitals roughly apart and a orbital that overlaps oxygen to make the bond. The carbonyl oxygen withdraws density, the bond weakens, and the hydrogen becomes acidic. A monocarboxylic acid has the general formula $CnH{2n}O_2$. IUPAC replaces the parent alkane's terminal $-e-oic$ acid, so the family is the alkanoic acids, and the trivial names must be carried alongside the systematic ones: methanoic (formic), ethanoic (acetic), propanoic (propionic), butanoic (butyric), pentanoic (valeric), hexanoic (caproic). Dicarboxylic acids add $-dioic$ acid, so $HOOC-COOH$ is ethanedioic (oxalic) acid and $CH_2(COOH)_2-oyl$ chloride, an alkyl alkanoate, or $-amide$.
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