I was trying to compare some solubilities (in water) and some boiling points, and I could not explain it for some molucules. Also, I have some doubts in the theory itself. Why is 2-pentanone more soluble than pentanoic acid? Why is a ketone more soluble than the respective aldeyde? When I compare boiling points, I was tauch to compare the interactions between the molecules, and the size of the molecule. How can I justify the size of a molecule interfering in solubility? I have 2 theories but I realy don't know if any of them are right. First I would say a big molecule would do more interactions than sa smaller one, so the boiling point should be greater. Also I would say that at the same temperature, all molecules has the same kinetic energy, and how kinetic energy is something like mv²/2, big molecules should have less velocity, so it would be harder for them to escape the liquids. Is it right? Another doubt I had was when I had to compare solubility. In this case I know the number of hyfrogen bond is important. Is the size important in this case too? In an exercise of my chemistry school book I was asked to compare the solubility of acetylsalicylic acid and salicylic acid. http://upload.wikimedia.org/wikipedia/commons/6/67/Aspirin-skeletal.svg http://upload.wikimedia.org/wikipedia/commons/8/8e/Salicylic-acid-skeletal.svg The first one makes 9 hydrogen bonds with water (is it right?) and has a bigger size (more interaction) also, the second one makes only 8 hydrogen bonds and has a smaller size. The answer, though, says that salicylic acid has a greater solubility. Why is this true?