Question

Hi, I was wondering if anyone could help me understand this? I keep getting asked if a molecule is soluble in water or hexane, how would I know?

Answer 1

mean by doing experiment or without doing experiment ??? you want to tell that

Answer 2

Without

Answer 3

based on polarity of molecule and polarity of solvent you can say that

Answer 4

Oops meant compound

Answer 5

if both are polar then they are soluble e and if bot are non polar then they are soluble

Answer 6

yaaa ur right

Answer 7

if one is polar and other one is non polar it is difficult to get soluble

Answer 8

any doubt in ur mind please free to share it ...

Answer 9

So for example, CH3CHCH2

Answer 10

The answer is hexane, but why?

Answer 11

its propene right its gas it is less soluble in water compared to organics bcoz it s not soo polar

Answer 12

hexane is non polar and propene also not sooo polar hence it can be soluble in hexane and not water

Answer 13

polarity in amolecule could be due to functional groups like -OH , SO3H , NH2 , - COOH etc

Answer 14

above statement is not universal
but most of the time its true !!!

Answer 15

actually, I was looking at the other compounds I had to do this for and noticed that the two that matched with hexane did not hydrogen bond like the only one that bonded with water, I think that might be the main thing.... thankyou

Answer 16

ur welcome :)

Answer 17

The solubility of any compound depends on the principle of LIKE DISSOLVES LIKE. This means that in a covalent compound (like hexane), only another covalent compound can dissolve. Similarly, in an ionic compound (like water), only an ionic compound can dissolve. Though there are exceptions, but the basic principle remains the same.

Answer 18

@Vaishnavireloaded

Water is not an ionic compound it is neutral.

@Vane11
I recommend looking through your text book for the section that covers hydrogen bonding and water, or you can check this page out:
http://www.chem1.com/acad/webtext/states/water.html

This stuff is fundamental to chemistry as well as biology. It is also important to know that water is able to form very strong intermolecular interactions with itself through hydrogen bonding.

If we were to introduce a non-polar molecule such as CH3CHCH2 (see below for an explanation why it is non-polar) into water it would disrupt the hydrogen bonds formed between water, it instead forms weaker dipole-induced dipole interactions (basically the electrons in the CH3CHCH2 molecule get pushed to one side of the molecule resulting in it having an induced polarity allowing it to form favorable interactions with water molecules). So one of the reasons it is insoluble is because water would rather hydrogen bond with itself as it is a more stable and thus a lower energy interaction than dipole-induced dipole interaction, the other reason has to do with entropy (the measure of disorder in a system), for water to form interactions with CH3CHCH2 it has to form an ordered solvation shell around the non-polar molecule, this is unfavourable! Something you should always keep in mind is that in our universe entropy is always increasing, meaning that as time passes disorder of the universe increases, for ever increase in order there must be a greater or equal increase in disorder.

Essentially water is just going to push the CH3CHCH2 molecules out of it, due to the reasons explained above.

As for determining if a compound is water soluble, it can be a bit more tricky, you have to look at the groups present on the molecule and make a guess at their polarity.

For instance,

CH3-OH or methanol this is water soluble because the oxygen carbon bond is very polarized, oxygen being very electrophilic will pull electron density away from the carbon giving it a partial positive charge. The oxygen can also act as a hydrogen bond acceptor, and the hydrogen can act as a hydrogen bond donator, therefore it can form favorable dipole dipole and hydrogen bonding interactions with water.

Another example would be

CH3-NH2 or methylamine, again CH3-NH2 will be polarized due to the electronegativity of the nitrogen atom, so it can form dipole dipole interactions with water. The partially negative charged nitrogen can act as a hydrogen bond acceptor and the two hydrogens attached to it can act as hydrogen bond donors to form favorable interactions with water.

But Beware

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2-OH, this molecule will not be soluble in water due to the long non-polar chain.


It should also be noted that non-polar compounds do form intermolecular interactions with themselves called london dispersion forces you are free to look them up but they are the weakest of the intermolecular interactions, but they can add up.


Sorry for the huge essay hope this helps if you have any questions please ask, if you are too lazy to read this I recommend reading up on intermolecular interactions and learning them all, also you may want to read up on electronegativity. Essentially go over the trends in the periodic table (atomic radius etc). This stuff is fundamental to chemistry and will make everything a lot easier to understand

If you have any questions feel free to ask.

Answer 19

LOL:(

Answer 20

what?

Answer 21

please give the explanation as much as small !!!:(

Answer 22

My explanation is pretty short actually, I included examples which added to the length significantly.

Answer 23

good !!!i am not denying that LOL:) but still you know:)