To obtain a soluble substance from a solution should the solution be concentrated? For example obtaining sugar from a sugar solution.
This question is full of holes. By concentrated to you mean
a. The sugar solution should have a high number of grams/volume, or
b. The sugar solution should have some of the solvent removed by evaporation.
If I had a sugar solution and I want to obtain pure sugar from that I would use b and evaporate some of the solvent. But you must be careful how you do that. Evaporating the solvent by boiling it away probably is a good idea for that will tend to hydrolyze some of the sugar and you will end up with some sugar, some glucose, and some fructose. Better to use a vacuum evaporator so as to preclude the hydrolysis.