 The acid functional group is able to form hydrogen bonds both through the OH group like an alcohol and through the carbonyl oxygen like a ketone or an aldehyde. So in liquid carboxylic acids this means that the molecules can orient themselves in pairs forming two hydrogen bonds that bind the pair together. So for instance a hydrogen bond could form between the carbonyl oxygen one molecule and the hydrogen on the OH group of another and simultaneously the other way around. So this pair of hydrogen bonds kind of binds these two molecules together in a little pair. When carboxylic acids are dissolved in water the acid molecule is also able to form multiple hydrogen bonds with the water molecules. So for instance we could have a hydrogen bond between the carbonyl oxygen and this hydrogen between the hydrogen of the OH group and the oxygen of the water. The oxygen of the OH group and the hydrogen of another water like this. So each carboxylic acid is able to form quite a few hydrogen bonds with surrounding water molecules. Because of this high level of hydrogen bonding carboxylic acids naturally have high boiling points significantly higher than alcohols. And this gives the general trend of boiling points here. Carboxylic acids have higher boiling points than alcohols which are higher than aldehydes and ketones which are higher than alkanes. As long as you're comparing molecules with the same number of carbons. Note that this is an example where understanding what's going on will save you some of the grief of memorizing. If you're able to remember this bond series here that hydrogen bonds are stronger than dipole-dipole attractions which are stronger than van der Waals forces. You can then work out from first principles which functional groups will have the highest boiling points by thinking about which intermolecular bonds a particular molecule is able to undergo. Turning to the solubility of acids in water as with many of our other homologous series the shorter acids are completely miscible. And also as with the other homologous series there comes a point when the hydrophobic nature of the non-polar carbon chain outweighs the ability of the acid group to form hydrogen bonds and the acid becomes insoluble. With aldehydes this begins to happen at propanel here, so a chain of three carbons. For alcohols it happens at butanol, so a chain of four carbons. And for the acids, because the acid group is able to form so many hydrogen bonds it actually doesn't occur until pentanoic acid, so a carbon chain of five.