Suppose I am trying to dissolve a compound into a minimal amount of solvent (let's assume that this compound is not pure and its impurity is not soluble in the solvent). So I have this compound in a glass and I slowly add the solvent, waiting until my compound is dissolved. How do I know that what isn't dissolved yet is the impurity and only the impurity? Perhaps some of what is not dissolved yet is my compound which I am trying to isolate but I need more solvent to dissolve it. How am I to know? Also, if after dissolving my compound and the solution is murky, does this mean that not everything is fully dissolved? i.e. I should filter the solution so that it's clear?