Ask A Scientist Chemistry Archive

name         Jessica W.
age          13

Question -   Okay, Here is a question. Can immiscible liquids become miscible? I have shaken up a 
mixture of water, alcohol, and oil. It seems to be mixing, and after three days it seems that it 
is still mixed together. Is it really mixed?
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Hello Jessica,

Thank you for that great question.  WATER and OIL by themselves are NOT SOLUBLE WITH EACH OTHER.  
Now you add an alcohol and MIX and BEHOLD they all seem to blend into one single miscible phase.  
You must be asking yourself, "This observation disagrees with what I have been told about WATER and 
OIL not dissolving into each other."  This is still a true statement... HOWEVER ...

The chemical with that magical touch (alcohol) is added to the mix and 'voila' you have a one phase 
solution.  W H Y  I S  T H I S  ??

I will tell you;

OIL(s):  Oil(s) are truly nearly 100% HYRDROPHOBIC (not liking water) compound(s)
WATER:  Water of course dissolves in itself (which makes sense)...so you could say that water is 
HYDROPHILLIC.

Now here is the answer that you have been looking for:  LIKES DISSOLVE LIKES....POLAR SOLVENTS 
DISSOLVE OTHER POLAR SOLVENTS (that is true enough).
The same is true with non-polar solvents (OIL) Where exactly does an alcohol fall into this range 
of POLAR vs. NON-POLAR
types of solvents?  I will tell you ... somewhere in the middle.  How is that for scientific.  There 
are many types of alcohols, but lets take for example PROPANOL (CH3CH2CHOH).  Looking at the 
structural formula for this alcohol, does not it make sense that this molecule (propanol) will have 
tendencies to be both POLAR (towards the ...CHOH side) and NONPOLAR (towards the CH3CH2C... side)???

Now consider the last statement very carefully, this ALCOHOL will dissolve in EITHER 1.) WATER and / 
or 2.) OIL.  Since this is true, OIL and WATER (along with some alcohol) can coexist in a one phase 
system since the NONPOLAR organic side of the alcohol is helping to dissolve the OIL and the POLAR 
side of the alcohol is helping to dissolve the WATER.  Think of the ALCOHOL as a sort of binder.  
Oil and water by themselves cannot stand each other.  However, alcohols help to bring these two 
together since WATER and OIL both like ALCOHOL.

Side note:  Alcohols, di-ethyl ether and many other solvents that exhibit nonpolar / polar solvation 
properties are used in reactions where COMPOUND A (only water soluble) needs to be dissolved and 
reacted with COMPOUND B (only oil / organic soluble).  A chemists will then perform what is called 
PHASE TRANSFER CATALYSIS.  He/She will add a "mediator" like your alcohol or an
either or whatever is best for the situation to get CMPD A and CMPD B within the same phase for a 
fast and efficient reaction.  Without this method, is certainly would be difficult to react POLAR 
molecules with NON-POLAR molecules, wouldn't it?

If you do not understand this explanation 100% then please drop another email.  We are always happy 
to hear from you.

Regards,
Darin Wagner
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Jessica,

If the components you describe form a completely clear solution with no trace of cloudiness, you can 
safely assume that they have "mixed." If, however, the results are even a little cloudy, what you 
have prepared is a rather stable emulsion -- components suspended as tiny globules in each other.

Depending on its exact composition (the ratio of oil to water to alcohol) it is likely that if given 
sufficient time, the emulsion will "break" and two components (oil and a solution of alcohol in 
water) will separate -- that is, they will "un-mix."

Regards,
ProfHoff 779
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Very probably, depending upon the relative amounts of each. Mixing an organic solvent that is 
miscible with water and with some water insoluble substance frequently causes the combination 
of the three to be soluble. Acetone is particularly 'good' at doing this because it is such a 
good solvent for many organic compounds that otherwise would not be very soluble in water alone.

Vince Calder
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You have an emulsion, with little drops of liquid dispersed in the other. Given enough time, it may 
separate (that's why stabilizers are added to foods like salad dressings).

Pat Rowe
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