Carboxylic acids have unusually high boiling points because in the liquid state their molecules
- A. are ionised
- B. form dimers held together by two hydrogen bonds
- C. form covalent bonds with one another
- D. are non polar
Explanation
Two molecules pair up so that the hydroxyl hydrogen of each bonds to the carbonyl oxygen of the other, giving a cyclic dimer with double the effective molar mass, so ethanoic acid boils at 118 degrees Celsius, well above ethanol despite similar size. The same dimerisation occurs in non polar solvents and even in the vapour just above the boiling point. Only in water do the dimers break up, replaced by hydrogen bonds to the solvent.
Related questions
The presence of chlorine atoms on the carbon next to the carboxyl group, as in chloroethanoic acid, makes the acid stronger because chlorine
Reduction of a carboxylic acid with lithium aluminium hydride gives
Which acid is the strongest?
Methanoic acid differs from other carboxylic acids in that it also
Carboxylic acids up to four carbon atoms are completely miscible with water because