Question

4. How do you decide whether to use enough hot water to dissolve acetanilide or enough to dissolve phenacetin?

5. If someone mixed sand into your unknown sample so you could not separate the grains of sand from the unknown solid, how could you separate them? Would the same action work if sucrose was mixed into your unknown?

6. Why would you allow the filtered liquid to cool slowly? What would happen if you did not allow slow cooling?

7. Why and when would you put the recrystallizing solution in an ice bath?

Answer 1

First of all, you'll need to put the background of all this question, in that way I could better understand the meaning of all the questions. There are questions like question 4, that I don't know if that question came from an experimental practice or something else.

In any case, I'll try to answer your question.

Question 4. That depends of what you actually wants, and depends of the solubility rate of both compounds. If acetanilide has more solubility than phenacetin, then I will use hot water to dissolve that compound and then recristallyzing that compound. If it's not the product that I want, then I'll have to separate both compounds by dissolving one of them (the more soluble) and then dissolving the another one in hot water. But basically that depends of what you actually want. I need more information about this question so I can answer it propperly.

Question 5. Basically the sand it's not soluble in water, so if my unknown sample is soluble in water (Hot water), then, I'll dissolve my sample in water, and then I'll filter the liquid. In that way, I can separate both solids. If it's not soluble in hot water, then I'll have to use a solvent where I can dissolve my sample and the sand do not dissolve and then, filter. With the sucrose, I could use a similar process, because if the sample it's not soluble but the sucrose does, (as it actually does), then I'll dissolve the sample with sucrose in water and then, filter.

Question 6. Basically because if you want to make a recrystallizing process the coolness should be slow so the crystal appears in a wide and better range and you'll get an even better yield. If it's not cool slowly then recrystallizing process doesn't take along well.

Question 7. you put a recrystallizing solution in ice bath when your solution does not recrystall properly solowly. So the ice bath acts like a catalizer, and speed up the reaction so the crystals may appear.