A student determined that ethanol was the best solvent to use for a recrystallization based on small scale trials. When the recrystallization was carried out on a larger scale, no crystals were obtained on cooling the hot solution.

Why? and how would you overcome this problem???

The reason why no crystals were obtained on cooling the hot solution during the recrystallization on a larger scale might be due to the fact that the solvent, ethanol in this case, might not be cooling down slowly enough.

During small scale trials, it is easier to control the cooling rate because there is less volume of solution involved. However, when performing a recrystallization on a larger scale, there is a higher volume of solution that needs to cool down, which can result in a faster cooling rate. This faster cooling rate can prevent the formation of crystals because the solute molecules do not have enough time to properly organize and form a crystal lattice structure.

To overcome this problem, you can try the following:

1. Slow down the cooling rate: One way to achieve this is by using a larger container to increase the surface area of the hot solution exposed to the air. This will promote a slower cooling rate, allowing the solute molecules to arrange themselves into a crystal structure.

2. Use a seed crystal: Adding a small amount of previously obtained crystals to the hot solution can act as a seed to initiate crystal formation. The seed crystal provides a starting point for the solute molecules to align themselves and grow upon, enhancing the chances of successful recrystallization.

3. Concentrate the solution: If the hot solution is too dilute, the solute molecules may be too far apart to effectively interact and form crystals. In this case, you can evaporate some of the solvent to increase the solute concentration, which can facilitate crystal formation upon cooling.

4. Try a different solvent or solvent mixture: If none of the above methods work, it might be worth exploring alternative solvents or solvent mixtures. Different solvents have different solubility properties, so choosing a more suitable solvent can help improve the chances of successful recrystallization on a larger scale.

Remember, when troubleshooting issues like this, it is important to document and analyze the experimental conditions and results carefully to identify the possible causes and potential solutions.