Biochem

[Swoops]

Hey I encountered this problem and was wondering if anyone could help me with it.

Which of the following molecules would you expect would form a micelle?
1. CH3COO–Na+
2. CH3(CH2)10COO–Na+
3. CH3(CH2)10CH3
4. CH3CH2CH2OH
Select one:
a. 3 only
b. 1, 2 and 4
c. 4 only
d. 2 and 3
e. 2 only

I know that a micelle has to have a polar and non polar region, and that the non polar region has to be significant. I have thus eliminated 1, and 4 base on the fact that it is an alcohol which would form a micelle. Also, 3 is non polar throughout so it can't be that. 2 is the only one that looks applicable to me. Could anyone confirm this? thanks in advance!

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[412smb412]

Hey I encountered this problem and was wondering if anyone could help me with it.

Which of the following molecules would you expect would form a micelle?
1. CH3COO–Na+
2. CH3(CH2)10COO–Na+
3. CH3(CH2)10CH3
4. CH3CH2CH2OH
Select one:
a. 3 only
b. 1, 2 and 4
c. 4 only
d. 2 and 3
e. 2 only

I know that a micelle has to have a polar and non polar region, and that the non polar region has to be significant. I have thus eliminated 1, and 4 base on the fact that it is an alcohol which would form a micelle. Also, 3 is non polar throughout so it can't be that. 2 is the only one that looks applicable to me. Could anyone confirm this? thanks in advance!

O makes the region polar and ch3 is non polar. So I would say 1,2,4

 

[aqz]

I would say 2 only.

This is based on an answer from achiever or topscore, can't remember which but...

Basically they said that any alcohols 4 carbons and under (meaning butane, propanol, ethanol, methanol) are all dissolvable in water, meaning a carbon chain 4 carbons or under is not going to affect the polarity enough to distinguish a non-polar region from a polar region.

So yes, 2 only.

 

[molarseeker]

I'd say 1, 2, 4 as well but its hard to tell how non polar that region will be. Does anyone know if there is a rule for how long the carbon chain should be?

 

[412smb412]

I would say 2 only.

This is based on an answer from achiever or topscore, can't remember which but...

Basically they said that any alcohols 4 carbons and under (meaning butane, propanol, ethanol, methanol) are all dissolvable in water, meaning a carbon chain 4 carbons or under is not going to affect the polarity enough to distinguish a non-polar region from a polar region.

So yes, 2 only.

i have read that as well but miscible means that there is a polar and non-polar region, but solubility is different. if it is soluble and has a non-polar and polar region it is miscible in water.

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

 

[aqz]

i have read that as well but miscible means that there is a polar and non-polar region, but solubility is different. if it is soluble and has a non-polar and polar region it is miscible in water.

So does that mean you agree that it's 2 only? If not, then I just don't understand the argument.

You agree that a micelle has to have a polar and nonpolar region. You also claim that you've heard about the 4 and under hydrocarbon chain rule....meaning that anything above butanol is "immiscible" in water -due to- the fact that although they have a polar hydroxy group, they also have a significantly nonpolar region. Anything 4 and below has an insignificant amount of hydrocarbon to make a nonpolar region, leading to a purely polar substance that is miscible in other polar stuff because it has no significant nonpolar-ness.

I also don't see the point for solubility. Your link has an example for diethyl ether...stating that it's soluble in water but not miscible...but micelle formation is only dependent on a substance having distinct polar/nonpolar ends.

Lastly, I have never seen an example of a micelle having one methyl as its "hydrocarbon tail". In most definitions, micelle has a "long hydrocarbon tail". If you can find an example of a micelle with 2 carbon chain tails, please let me know.

 

[412smb412]

So does that mean you agree that it's 2 only? If not, then I just don't understand the argument.

You agree that a micelle has to have a polar and nonpolar region. You also claim that you've heard about the 4 and under hydrocarbon chain rule....meaning that anything above butanol is "immiscible" in water -due to- the fact that although they have a polar hydroxy group, they also have a significantly nonpolar region. Anything 4 and below has an insignificant amount of hydrocarbon to make a nonpolar region, leading to a purely polar substance that is miscible in other polar stuff because it has no significant nonpolar-ness.

I also don't see the point for solubility. Your link has an example for diethyl ether...stating that it's soluble in water but not miscible...but micelle formation is only dependent on a substance having distinct polar/nonpolar ends.

Lastly, I have never seen an example of a micelle having one methyl as its "hydrocarbon tail". In most definitions, micelle has a "long hydrocarbon tail". If you can find an example of a micelle with 2 carbon chain tails, please let me know.

i believe it is 1,2,4. go to the wikipedia link: http://en.wikipedia.org/wiki/Miscibility. it says octanol is immiscible but ethanol is miscible.

"In organic compounds, the weight percent of hydrocarbon chain often determines the compound's miscibility with water. For example, among the alcohols, ethanol has two carbon atoms and is miscible with water, whereas octanol with a C8H17 substituent is not. Octanol's immiscibility leads it to be used as a standard for partition equilibria. This is also the case with lipids; the very long carbon chains of lipids cause them to almost always be immiscible with water."

1. needs to have both a polar and non-polar end
2. needs to be less than 4 carbons

if it satisfies both it is miscible, thats what i get from this...

 

[aqz]

I think you're missing the point.

I -completely agree- with your 2 criteria that it will be miscible...

However, that has -nothing- to do with whether a substance will form a micelle. The only thing that being "miscible in water" has to do with "forming a micelle" is that it determines whether the substance will be polar, nonpolar, or have a nonpolar AND a polar side.

If the given substance is a hydrocarbon chain with a polar functional group (such as alcohol or Na+):

-Being miscible in water = the substance is considered polar because the hydrocarbon chain is negligible. Therefore, it ONLY has a polar end, and will not form a micelle.
-Being immiscible in water = the substance's nonpolar end is no longer negligible. Therefore, it has both a nonpolar end AND a polar end and thus will form a micelle.


You can apply this to your own example above with ethanol and octanol. Because ethanol is miscible with water, it only has a polar end = it will NOT form a micelle because micelles require a polar AND a nonpolar end.

Octanol, on the other hand, has a nonpolar end that's long AND significant enough along with a polar functional group to form a micelle.

Sorry for dragging this out, but I stand by my point that being miscible has no direct correlation to forming a micelle. Bottom line, find me a micelle containing a hydrocarbon chain that has 4 carbons or less.

 

[412smb412]

I think you're missing the point.

I -completely agree- with your 2 criteria that it will be miscible...

However, that has -nothing- to do with whether a substance will form a micelle. The only thing that being "miscible in water" has to do with "forming a micelle" is that it determines whether the substance will be polar, nonpolar, or have a nonpolar AND a polar side.

If the given substance is a hydrocarbon chain with a polar functional group (such as alcohol or Na+):

-Being miscible in water = the substance is considered polar because the hydrocarbon chain is negligible. Therefore, it ONLY has a polar end, and will not form a micelle.
-Being immiscible in water = the substance's nonpolar end is no longer negligible. Therefore, it has both a nonpolar end AND a polar end and thus will form a micelle.


You can apply this to your own example above with ethanol and octanol. Because ethanol is miscible with water, it only has a polar end = it will NOT form a micelle because micelles require a polar AND a nonpolar end.

Octanol, on the other hand, has a nonpolar end that's long AND significant enough along with a polar functional group to form a micelle.

Sorry for dragging this out, but I stand by my point that being miscible has no direct correlation to forming a micelle. Bottom line, find me a micelle containing a hydrocarbon chain that has 4 carbons or less.

No you're right. I made a mistake. Ethanol is miscible but does not form micelles, didn't see the difference btwn 'micelle and misciblle' at first but now I do.


Now i see the answer is 2 only!
thanks