Which of these substances is the least soluble in water?

[MoMo Morgan]

Homework Statement

Which of the substances below is least soluable in water?

A. CH2OHCHOHCH2OH
B. CH3COCH3
C. CH3CH2COOH
D. CH3COOCH3

Homework Equations

The Attempt at a Solution

I think bith B and C are not possible since B can dissolve in water easily and C is acid which is soluable in water. But i don't know what to choose from A and D. I checked on the Internet, it says D is not easy to dissolve in water, but my teacher told me he thinks A or B will be the answer. I totally think he is wrong at this point. Can anyone help me out with this?

 

[Gannon]

The least soluble will be the one that is least polar; A and C will readily dissolve because of the OH groups, so it's between B and D. I think esters would dissolve more readily than ethers, so I would choose B, but I could be wrong.

 

[MoMo Morgan]

Hi there thanks for the reply, I think the answer is B, you are right.

For the comparison of B and D, I just found an answer

"Esters participate in hydrogen bonds as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding makes them more water-soluble than their parent hydrocarbons. "

http://en.wikipedia.org/wiki/Ester

And by the way, C is a COOH group (carboxylic acid) instead of OH.

thank you for your help.

 

[Gannon]

I'm not sure what Wikipedia means by "parent hydrocarbons" since an ester is usually formed by combining a carboxylic acid with an alcohol. But I found this:

"Ethers are less polar than alkenes but not as polar as alcohols, esters or amides of comparable structure..." It goes on to state that cyclic ethers are more water-soluble than non-cyclic ethers.

This would support B as the right answer.

 

[MoMo Morgan]

I just realize B is ketone, not ether.
Ketone is highly soluable in water.

So the answer will be D?

 

[Kushal]

esters are not miscible with water. they form a separate oily layer. it is D.

A is glycerol. it has a relatively low Mr. it forms H-bonds in water, and is therefore soluble.

 

[chemisttree]

Kushal is correct.

 

[MoMo Morgan]

I have another question.
What does the text mean by ester is more water-soluble than their parent hydrocarbons?
I thought the parent hydrocarbons refer to alcohol and carboxylic acid.

 

[chemisttree]

Poorly worded. It should mean that an ester based on 12 carbons (total) is more water soluble than a hydrocarbon with 12 carbons. Not a very useful statement in my opinion since esters are not generally recognized as being 'soluble' in water but water does have an affinity for esters and will dissolve in them at the rate of several hundreds of parts per million.

I have seen that language also used (more correctly) to describe the solubility of alcohols. It is true that alcohols are more soluble than their parent hydrocarbons. The statement attibuted about esters coming at the heels of a statement about alcohols further confuses the issue... not good teaching in my opinion.

 

[MoMo Morgan]

Thank you so much for your reply. It helps me a lot! :)