consider a crystallization of sulfanilamide in which 10 mL of hot 95% ethyl alcohol is added to 0.10 g of impure sulfanimide. after the solid has dissolved, the solution is cooled to room temp. and then placed into an ice-water bath. no crystals for, even after scratching with a glass rod. explain why this crystallization failed. what would you have to do at this point to make the crystallization work?

Is there any reason not to evaporate the alcohol off?

To add to Bob Pursley's great answer the probable reason you had no crystal formation was that the compound was too soluble in the alcohol.

I understand that thecompound was too soluble but what about the second part of the question? What would you have to do to make the crystallization work? Would one just have to retry the crystallization, or find a different solvent?

You need to induce crystallization by seeding it. Get a crystals of the original solid and placing it in the solution. Crystals should form. Another form is by taking a glass rod and dipping it in the solution and then taking it out to let the alcohol evaporate. Crystals will form on the rod, these crystals can then be used for the seeding purpose. hopes this makes sense and helps

atsud

The crystallization process failed because the solution did not cool down slowly enough, which prevents the formation of crystals. To make the crystallization work, you need to follow these steps:

1. Slow cooling: The solution needs to be cooled down slowly to allow the sulfanilamide molecules to come together in an organized manner and form crystals. Rapid cooling, as in this case, does not provide enough time for the molecules to arrange themselves into a crystal lattice structure. You mentioned that the solution was cooled to room temperature and then placed in an ice-water bath. Instead, you should cool the solution slowly to room temperature and then leave it at room temperature for a considerable amount of time, ensuring a slow and controlled cooling process.

2. Seeding: Sometimes, the solution requires a starting point for crystal formation. This can be achieved by adding a small amount of previously prepared pure sulfanilamide crystals to the solution. The added crystals act as nuclei or "seeds" for the impure sulfanilamide molecules to attach onto and grow into larger crystals.

3. Scratching: If there is no crystal formation even after slow cooling and seeding, you can try using a glass rod to scratch the sides or bottom of the container. Scratching provides a rough surface where crystal growth can initiate. By scratching, you create tiny imperfections or "seeds" on the glass surface, promoting crystal nucleation.

4. Concentration: If the concentration of sulfanilamide in the solution is too low, it might hinder the formation of crystals. In this case, you can try evaporating some of the solvent (ethyl alcohol) by gentle heating to increase the concentration of sulfanilamide. Be cautious not to apply excessive heat, as it could cause the sulfanilamide to decompose.

Remember, the success of crystallization depends on several factors, such as appropriate cooling rate, seeding, scratching, and concentration. Adjusting these variables can often improve the chances of successful crystallization.