boiling point?

Question

why solubility at 20 degree goes down but boiling point goes up
CH3-OH
CH3-CH2-OH
CH3-CH2-CH2-OH
I think they have the same kinda bonding like hydrogen bond , different is the bonding on the middle
i think the third molecule have more bonds therefore they need more energy to break the bond that implies boiling point goes up but im not sure my answer

Answer 1

The solubility goes down because you are introducing a longer hydrophobic "Stick" into the molecule with increasing chain length.

HO——
HO————
HO————————

The boiling point increases because the molecule is getting bigger. With increase in mass you get an increase in boiling point with no other influences on the system.

Compare CH4 to C6H14

Answer 2

Your answer for the trend in boiling point sounds correct.

Trend in b.p: Methanol < Ethanol < Propanol

The longer the carbon chain, the more energy needed to break the bonds in the molecule, hence higher boiling point.

Answer 3

The longer the carbon chain, the more the hydrophobic properties (water-hating) takes over. All the molecules have an -OH group, which forms hydrogen-bonds with water, but this attractive force is outweighed by the water-hating properties of the longer and longer carbon chain.