Everything from the 2 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
Carboxylic acids are the strongest of the O–H acids: carboxylic acid > phenol > water > alcohol, because the charge of the carboxylate ion is shared equally over two O atoms. Anything that stabilises RCOO− further makes the acid stronger. Electron-withdrawing Cl atoms pull electron density away from the COO− group and spread its charge: the more Cl atoms, and the closer they are to the COOH group, the stronger the acid (pKa ethanoic 4.76, chloroethanoic 2.86, dichloroethanoic 1.29, trichloroethanoic 0.65). Electron-donating alkyl groups destabilise the anion, so ethanoic acid is weaker than methanoic acid. Methanoic acid, HCOOH, still has an H on its C=O carbon, so it is oxidised to CO2 by Tollens', Fehling's and acidified KMnO4; ethanedioic acid decolourises warm acidified KMnO4, giving CO2.
Electron-withdrawing groups make an acid stronger; electron-donating groups make it weaker. The explanation must be about the stability of the carboxylate anion, not about the O–H bond alone. More Cl is stronger, and Cl closer to the COOH group is stronger. A smaller pKa means a stronger acid. Of the simple carboxylic acids, only methanoic gives positive Tollens' and Fehling's tests; ethanedioic acid needs warm acidified KMnO4.
An acyl chloride, RCOCl, is made from a carboxylic acid with PCl5 (room temperature), PCl3 and heat, or SOCl2. Its carbonyl carbon is bonded to two electronegative atoms, O and Cl, so it is strongly δ+ and planar, open to attack by nucleophiles. Acyl chlorides react by nucleophilic addition-elimination: a lone pair adds to the C=O carbon, then the C=O reforms and Cl− leaves with H+ as HCl. With water they give the carboxylic acid (vigorous, steamy HCl fumes); with alcohols and phenols, esters; with ammonia and amines, amides. Ease of hydrolysis: acyl chloride >> chloroalkane > chlorobenzene.
Show the mechanism in two steps: addition (lone pair to C, C=O π electrons to O) then elimination (C=O reforms, Cl− leaves). Start every curly arrow from a lone pair or a bond, never from an atom or a charge sign. The by-product is always HCl (or its ammonium salt), not water. Chlorobenzene is the hardest to hydrolyse, not the easiest: its C–Cl bond has partial double-bond character.