Getting the Solid Back: Evaporate, Crystallise, and Dry to Constant Mass

Use a wide, shallow evaporating dish rather than a beaker: evaporation happens at the surface, so the area is what sets the speed, and a wide dish is faster at a much lower temperature. Stop while a little liquid remains and let the rest go at room temperature. Once the liquid is nearly gone there is nothing left to absorb the heat, the solid overheats in seconds, and it spits, decomposes or bakes onto the dish. A steam bath or a hot plate on a low setting is better than a flame for anything that matters. Direct flame heats one spot far above the boiling point of the solution, and many substances that survive 100 degrees do not survive that.

Dissolve the solid in the smallest volume of hot solvent that will take it, then let it cool UNDISTURBED. Slow cooling grows few, large, pure crystals; rapid cooling or stirring gives a mass of tiny ones that trap the mother liquor and everything dissolved in it. If nothing appears, it is usually because there is too much solvent or because there is no nucleus to start on. Boil a little solvent off, scratch the inside of the glass with a rod at the surface, or add one seed crystal. Then filter the crystals off cold and rinse them with a SMALL amount of ICE-COLD solvent. Rinsing with warm solvent dissolves the product you just spent an hour growing, which is the most disheartening way to lose a yield.

Percentage yield is what you got divided by what the equation says you could have got. Both numbers have to be real: the mass actually recovered and dried, and the theoretical mass calculated from the LIMITING reagent. Yields above 100% mean the product is not dry, or it has picked up something. That is worth treating as a fault rather than a bonus, because a wet product weighs more and is worth less. Record where the losses went, in the notebook: left in the mother liquor, stuck to the filter paper, lost in the rinse, spilled. Those lines are what make the next attempt better, and a yield with no explanation attached is a number nobody can improve.