4.5 carboxylic acids

Question 1

why are boiling point higher in carboxylic acids than alcohol? and how does h-bonding occur between two molecules to produce a dimer? and in water?

Answer 1

• c=o has a permanent dipole so more vdw
• as well as having OH so hydrogen bonding too
• two c’acids join so there is h-bonding on both sides (reflect one of them)
• don’t form diners in h20 only h-bonds

Question 2

why are c’acids acidic?

Answer 2

• has h+
• CH3COOH(aq) —> CH3COO- (aq) + H+(aq)
• ka smaller than 1 the weaker the acid as it’s less dissociated
• larger pka weaker the acid smaller ka weaker the acid

Question 3

why is phenol acidic?

Answer 3

stable ion formed by delocalisation extending over
phenol + water = phenoxide ion and h30+
phenol | c’acid
add na2co3 | add na2co3
no reaction | bubbles of co2 gas
not acidic enough | reacts freely cuz more acidic

Question 4

what is hydrolysis?

Answer 4

• breaking a ester into c’acid and alcohol
• you can go backwards in the reverse reaction but
• better method is to reflux with naoh
  eg: ethyl ethanoate + naoh —> sodium ethanoate + ethanol
• then add hcl to sodium salt
• to make c’acid

Question 5

what is decarboxylation? conversion of carboxylic acid into alkane

Answer 5

removal of cooh from c’acid
when a c’acid or sodium salt is heated with hot solid naoh (soda lime)

Question 6

method of recrystallisation

Answer 6

• add minimum amount of hot solvent to dissolve crystals (too much solvent and crystals won’t form)
• cool mixture so crystals reform but impurities remain in solvent
• carry out suction filtration to remove solvent and leave crystals behind
• allow to dry
• carry out melting point analysis
• the closer the solid to the melting point in the data book, the more pure it is