Question

Why is ethanol soluble in water?

Answer 1

Ethanol is soluble where as larger molecules of a seemingly similar type do not. It's about the overall polarity (or electrical balance) of the molecule. The hydroxyl group plays the main role in allowing it to be tied to a H2O molecule but the added hydrocarbon chains start to degrade that polarity. Ethanol has an overall polarity that allows it to make hydrogen bonds to water easily, allowing solubility. Methanol, ethanol and propanol have just less enough hydrocarbon chains to make the -OH to H2O bond possible (i.e. soluble). Once that fourth(?) carbon comes in to play the electrical balance shifts and it no longer allows the end -OH to make a hydrogen bond to water. The reason, the electro balance takes "power" away from the -OH end not letting it bond to the H (in H2O) as it normally would. Now the molecule is more "stable" or "apolar". The electrons in the molecule make the the unsettled -OH chill out and allow balance internally, not seeking recognition from the outside, such as from the always polar H2O molecule. So you can imagine in it like the more you add hydrocarbon chains to it, the more it takes solubility away from it. -OH loses it's touch as the molecule has a longer chain, balancing against that polar end