Carboxylic acids are molecules with trigonal planar geometry. They have acidic hydrogen in the hydroxyl group and behave like bases on carbonyl oxygen.

physical properties 01
 
O : basic oxygen
H : Acidic hydrogen
 
The melting and boiling points are high since they form dimers, due to hydrogen bonding.
 
physical properties 02
 
Hydrogen bonds ( ------------ )
CH3COOH Boiling point: 118ºC
CH3CH2COOH Boiling point: 141.8ºC
 
 
Methanoic acid molecular model
methanoic acid
 
Ethanoic acid molecular model
ethanoic acid