Question

If two solutions with different densities are placed in a glass, and they form two layers, does this mean they are not soluble?

Answer 1

They are not mutually soluble. Solvents that form two layers are called `"immiscible"`

Explanation:

Hexanes and water, diethyl ether and water, methylene chloride and water, are IMMISCIBLE. There are many other examples. They form 2 separate layers, with the most dense solvent on the bottom. (There will be some water dissolved in the so-called organic layer, and some organic solvent in the water layer, but there will still be 2 bulk phases).

In the laboratory, often a solute is "partitioned" across 2 such phases. Organic solutes are collected in the organic layer, and inorganic solutes (ions etc.) are collected in the aqueous layer. Such a process is called "solvent extraction".