Propionic Acid, 1-Butanol and Water

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[chemnut]

Would propionic acid be more soluble in water or 1-butanol? My educated guess is that it would be more soluble in 1-butanol, due to the hydrogen bonding in both and the hydrocarbon chains in both. With the propionic acid/water solution, there is only hydrogen bonding.

As a follow-up to that question, is it more difficult to perform an extraction of a substance that is highly soluble in a solvent, or is it more difficult to perform an extraction of a substance that is only slightly soluble in a solvent?

Many thanks for any/all help!

[chrisf]

Propionic acid should be more soluble in water than n-butanol. Propionic acid has the hydroxyl group which makes the molecule polar and promotes its solubility in water. At the same time, the carbon chain resists the solubility.

n-butanol consists of a longer carbon chain that propionic acid while both have a hydroxyl group and I'm guessing but would the propionic acid be more polar as well because of the double-bonded oxygen? I'm not sure.

I'd say that it's more difficult to perform an extraction of a substance that is highly soluble in the solvent.. unless you're using the solvent as a 'wash' in which case you'll be discarding it and you want the substance to be highly soluble.

[chemnut]

Hmm... I was thinking about "like dissolves like", too, and that's why it seemed logical that propionic acid would be more soluble in 1-butanol.

Still pondering... thanks for your reply!

[valdorod]

Propionic acid should be more soluble in water than 1-butanol.

I think the question was between these two choices

propionic acid in water vs propionic acid in 1-butanol

I would have to agree with chemnut propionic and t butanol are both polar organic molecules.  while water is just polar and not organic.

I would also have to agree with chrisf for the second part, if using a separatory funnel for example, you would want to have two substances that are not very miscible so that they would separate.

[Otis]

Just a fly in the ointment but are you talking about solubility or miscibility? Is there a distinction in this question or is it poorly worded?

I wonder ...

Otis

[chemnut]

Thanks to all who've answered so far. I really appreciate it! Otis, you have hit on something that has been bothering me. I've seen "soluble" and "miscible" used interchangeably both in my lab manual and in other sources. I didn't think they were the same thing, but I'm not sure about that.

[valdorod]

Miscibility is a term that means soluble when relating two liquids, you can consider them synonyms.
When two liquids mix to an appreciable extent to form a solution, they are said to be miscible.  If they do not mix to form a solution they are immiscible.  The difference is that miscibility usually indicates a solution in which both the solute and solvent are liquids, and in rare instances when both are in the same phase, i.e. gas in a gas, solid in a solid or liquid in a liquid.

Why have two terms, well the term miscibility allows us to deal with a situation that is not present when you have a solid in a liquid or a gas in a liquid.

For mixed phase solutions there is always going to be a saturation point, at which point you have reached the solubility equilibrium and you cannot dissolve any more solute.  However, in same phase systems you have situation in which you have no saturation point.  For these systems you can continue to add the solute until eventually the solute becomes the solvent and the solvent becomes the solute.  Compare a 40% spirit vs an 80% spirit.

For example ethanol and water will dissolve in each other in any ratio.  When such is the case we say that the liquids are completely miscible.   Using the term completely soluble does or always soluble does not have that connotation.

When two liquids are partially miscible, it does not mean that they are partially soluble.  The two liquids are soluble, however, there is a saturation point, after which you have the liquids separate into layers.

I hope I did not make it more confusing, let me see if I can do an example.

Ethanol is soluble in water, thus we can say that they are miscible.
Salt is soluble in water.
1-butanol is soluble in water, thus we can also way that they are miscible.

You can continue to add ethanol to water and it will always dissolve.  You can continue to do so until you have more ethanol than water, then the water is called the solute and the ethanol the solvent.  We say that they are completely miscible in each other.

If you continue adding salt you will eventually have a saturated solution and you will not be able to dissolve any more salt after that.  It is still a solution and it is saturated.

If you continue adding 1-butanol eventually you cannot dissolve anymore butanol, you have a saturated solution.  We call these two liquids partially miscible.  The same way that adding more salt will give you two phases, one solid and one liquid, adding more butanol will give you additional phases, sometimes two sometimes three.

As an additional note, many times a solvent is described as being the substance in greatest amount.  That only applies when the solute and solvent are in the same phase.  For example at above 40C you can dissolve twice the grams of sugar as you have water, and even though you have more sugar, the water is still the solvent and the sugar is still the solute.

[chemnut]

Wow, thanks, Valdo! Gee whiz, some terms I thought were "simple" aren't so simple any more. Thanks so much for your detailed explanation.

[Otis]

Valdorod,
Thanks for the full explanation.

See if my simple statements work.

Miscibility is use for liquids that "mix into" each other in all proportions - a sliding scale of concentrations. Immiscibility means they do not mix at all and partial miscibility means they will reach some equilibrium of miscibility.

I'm not sure if you can use the miscible with regards to gases because they diffuse. Although you would expect some gradient of heavier gases due to the effects of gravity - low oxygen levels at high altitudes for instance.

Solids are soluble in liquids until the concentration of the solute is such that it reaches equilibrium with the solvent then additional solute becomes insoluble.

But, to return to the question of solubility of propanoic acid and n-butanol. Is propanoic acid the answer because of the smaller hydrocarbon chain or the carboxylic group having a greater negative dipole moment making it more polarized (my choice).

Still learning ...
Otis