# What is the solution and the solvent in 80% solution of ethanol in water?

I was wondering whether the solvent is water or ethanol, I think it must be ethanol because it is present in larger quantity; however, on the other hand water is the universal solvent so shouldn't it be the solvent.

• The solvent is ethanol. Since both ethanol,water and solution are in the same phase and ethanol is in greater proportion, it will be called as the solvent – Amritansh Singhal Sep 26 '16 at 7:00
• Of course the notion depends on context too. If I were studying a bunch of alcohols at different concentrations in water, then I would probably refer to water always as the solvent and whatever alcohol as the solute. Imagine trying to create a table and flipping from water being the solvent to ethanol. It would be really confusing. – MaxW Sep 26 '16 at 7:23
• You're severely misinterpreting the meaning of the phrase "universal solvent". All it means is that water can dissolve a lot of things, i.e. it can be a solvent for many chemicals. (And on top of that, that phrase is nearly always used in a biological context, because water is rubbish at dissolving most organic compounds.) It does not mean that water always takes on the role of the solvent. – orthocresol Sep 26 '16 at 9:06
• @orthocresol - Geologists and mineralogists "sometimes" use water too. It seems that in spite of the human preference for ethanol, mother earth likes water. – MaxW Sep 26 '16 at 16:25

## 1 Answer

Magical thinking, such as thinking that because a certain chemical has a certain name, that (absent a systematic nomenclature system which requires the name to correspond to certain properties) it will magically exert some unique influence, is almost always incompatible with science. There is no requirement that a green house must be green, nor that the "universal solvent" (both water and time are often called that) means everything dissolves in it. Logical analysis requires the recognition that "a rose by any other name will smell as sweet". That is, what something is called may or may not help to characterize it. Your question shows that you haven't discriminated between an 80% solution by mass fraction, by volume fraction, or by mole fraction - all of which are different compositions, in general. The more pointed question is if a mixture is exactly 50% of one, and 50% of the other is it a solution? And if so, which is the solvent and which is the solute? Note that the mass fraction is a conserved quantity (it doesn't change), but the volume fraction may not be a linear function of mass % (often abbreviated v/v and w/w, respectively (w is for "weight" even though chemists should know better) There are a variety of conventions which determine which of two liquids is the solvent and which is the solute. In dilute solution, the choice is obvious, but as concentration rises above 10%, there isn't necessarily one answer correct answer. Consider a solid dissolved in water at 80%. We'd still call that an aqueous solution. Even 80% sulfuric acid (not that "pure" sulfuric acid is a stable compound, but it should be considered a liquid (at STP) for most purposes) is generally considered an aqueous solution. Note that both of these solutions are quite un-water-like, compared to solutions where the solute is present at 0.1 molar or less (and is of fairly small molecular mass, say <1000 g/mole (but there's no definite cut-off)). Chemistry, more so than physics, is a pragmatic science. To give a good answer to your question, you'd have to explain the context you wanted to use "solvent" and "solute" in describing your mixture. The general rule of thumb is that the solvent is the continuous phase, but that answer has some problems (which I'll not go into here). A 1:1 mixture by moles would have 18g of water for every 46 g of ethanol or would be about 72 weight % ethanol. (EtOH/Water mixtures do not conserve volume, so that adding 28 ml of water to 72 ml of EtOH would result in less than 100 ml. But volume % is generally meant to imply volume of the starting materials rather than the volume each compound occupies in the mixture). So an 80% solution would mean that there's slightly more EtOH (by volume, much more by mass and slightly more by moles) than water. There are three perfectly valid answers: 1) EtOH is the solvent. 2)Each is dissolved in the other. 3)Water is the solvent. 4)It's better called a mixture than a solution, (even better a "homogeneous mixture"). Oh wait, did I say 3? LOL! To reiterate, as the concentration increases, it becomes less and less USEFUL to characterize one liquid (in a binary system) as the solvent and the other as the solute. So the answer is moot.

• I think you have very good points, but it could do with a bit of paragraphing. By the way, to make a new paragraph, you need to press Enter twice. – orthocresol Sep 26 '16 at 9:04