How do I know how much water to use in the recrystallization?
From the weight of the crude unknown, calculate the amounts of hot water needed to dissolve it if the unknown is acetanilide or if it is phenacetin. Since we will use the steam bath for heat, our temperature will be less than 100 °C and these estimated will be a bit low. Begin by assuming your unknown is the more soluble compound. Add the water in portions, and swirl on the steam cone for about a minute between portions, so you can see how much solid is dissolving. This will allow you to prepare a nearly saturated hot solution, while at the same time giving a clue as to the identity of the unknown (by its solubility). Remember that you want to avoid adding too much water. We’ll wash with just a small portion of boiling water (have some distilled water boiling on a heating mantle in a 100 mL round-bottom flask for this purpose – use boiling chips).
