If I dissolve table salt (NaCl) in water, it breaks down into Na+ and Cl- ions. If I then evaporate the water away, the ions recombine and I get my salt back, chemically identical to what I started with.
If I “dissolve” oil in ethanol, an then evaporate the ethanol away, do I get my oil back? Is the oil “dissolving” in the ethanol in the same sense that salt dissolves in water, or is something else going on?
Yes, you get oil back.
It’s a little different because oils aren’t ionic substances and don’t break down into separate + and - ions. The oil molecules wind up floating around as molecules. Also, when you’re combining liquids that mix perfectly, you can say they’re miscible, rather than naming a solvent and a solute.
Depending on the oil, you might lose some of it to evaporation. And as you remove ethanol, at some point you cross over from A dissolved in B to just a mixture of A and B, then B dissolved in A. Getting that last bit of ethanol out can take heat, vacuum, or sorbent. And depending on the oil and the conditions, you could have some reaction with ethanol.
Just an aside, alcohols don’t do a very good job of removing oils. Things like Stoddard Safety Solvent (basically kerosene) and 111 trichloroethane were our solvents of choice at NASA. Followed by an acetone rinse. One of my favorite products is Gunk. You mixed a small amount (5% maybe) with the solvent and then when you cleaned up the oil the whole mixture was now magically water soluble.
The Na+ and Cl- dissolved in water is an ionic solution.
Oil dissolved in ethanol is a covalent solution.
As an aside, it bugs me when high-school science textbooks say that dissolution is a physical change, not a chemical change. That’s true of molecular compounds like sugar, maybe, but dissolution of an ionic compound is absolutely a chemical change.
The idea of an absolute distinction between physical and chemical changes has always bothered me. Chemical changes are physical. There are multiple interactions at work when two atoms play together. It’s an oversimplification to pretend that only one type of interaction matters.
I do have to say, though, that AFAIK this is a minority opinion, and Chronos has the backing of nearly everybody who deals in chemistry.
I mean, the notion of an absolute distinction between categories is always fraught. The real world doesn’t work in nice neat boxes, no matter how much we might want it to.
And yeah, even if we do lump “sugar dissolving in water” in the category “physical change”, it’s still a much more extreme “physical change” than, say, shuffling a deck of cards.