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.
A carboxylic acid contains the carboxyl group, –COOH. It is made by oxidising a primary alcohol or an aldehyde with acidified K2Cr2O7, heating under reflux; by hydrolysing a nitrile with dilute acid under reflux (the C of the CN group becomes the COOH carbon); or by hydrolysing an ester. Carboxylic acids are weak acids: they only partly dissociate, RCOOH ⇌ RCOO− + H+. They still show all the typical acid reactions: reactive metals give a salt and hydrogen, alkalis give a salt and water, and carbonates give a salt, water and carbon dioxide. That fizzing with sodium carbonate is the test that separates them from alcohols. LiAlH4 in dry ether reduces them to primary alcohols.
Only carbonates and hydrogencarbonates separate acids from alcohols: sodium and PCl5 react with any –OH group. Carboxylic acids are weak (partly dissociated), not dilute; a weak acid still reacts completely with excess metal, alkali or carbonate. Keep the 2 : 1 acid to Mg and acid to Na2CO3 ratios. Reduction needs LiAlH4, not NaBH4, and gives a primary alcohol. A nitrile keeps its CN carbon, so count carbons carefully.
An ester, RCOOR′, forms when a carboxylic acid reacts with an alcohol, heated with a few drops of concentrated H2SO4 as a catalyst; water is the other product and the reaction is reversible. Esters are named alkyl alkanoate: the alcohol part first, then the acid part, so CH3COOC2H5 is ethyl ethanoate. Acid hydrolysis (dilute acid, heat under reflux) is the reverse of esterification and reaches equilibrium. Alkaline hydrolysis with NaOH(aq) under reflux goes to completion, giving the carboxylate salt and the alcohol, because the carboxylate ion cannot react with the alcohol. Fats and oils are triesters of glycerol (propane-1,2,3-triol); boiling them with NaOH is saponification and gives soap. Esters are used as flavourings, perfumes and solvents.
Name the alcohol part first: CH3COOC2H5 is ethyl ethanoate, and HCOOCH3 is methyl methanoate. Concentrated H2SO4 is a catalyst in esterification, but in alkaline hydrolysis the NaOH is a reactant that is used up. Alkaline hydrolysis gives the salt (RCOO−Na+), not the free acid, until you acidify. One fat molecule uses three NaOH and gives three soap molecules.