I am reading through material for a recrystallization experiment, and I had a few things I wasn't sure about;

- Why once filtered, should the recrystallization solution be allowed to cool slowly, undisturbed, rather than quickly?

and

-What makes a good solvent, i.e. what are the characteristics of a good solvent for recrystallization???

for the first ques, i think it that step should be done because it allows the crystals to form properly. ANy help appreciated.

You're on the right track. Crystals that can form slowly form more perfect crystals with fewer "contaminating" particles getting caught within the crystal lattice. Cooling slowly aids the more perfect crystal process.

For the solvent, you want one that will dissolve the solute at higher temperatures (below the solvents boiling point and below the melting point of the solute) but isn't too soluble at lower temperatures (so it will crystallize easily).

Thank you =)

When it comes to recrystallization, the process of allowing the recrystallization solution to cool slowly and undisturbed is important for several reasons.

Firstly, cooling the solution slowly helps in achieving a controlled and gradual decrease in temperature. This controlled cooling allows the molecules in the solution to come together in an organized manner and form an ordered crystal lattice. If the solution cools too quickly, then the molecules may not have sufficient time to arrange themselves into a well-defined crystal structure.

Secondly, allowing the solution to cool undisturbed ensures that the crystals can grow and form without any disruptions. Disturbing the solution while it cools, such as by stirring or agitating it, can introduce impurities or disrupt the crystal formation process. Slow, undisturbed cooling allows for the gradual separation of solute molecules from the solvent, enabling the formation of purer, larger, and more well-defined crystals.

Now, let's move on to the second question about the characteristics of a good solvent for recrystallization.

A good solvent for recrystallization should possess several important characteristics:

1. High solubility of the solute at an elevated temperature: The solvent should be capable of dissolving the desired compound at an elevated temperature to create a saturated solution. This ensures that the maximum amount of solute can be dissolved initially, increasing the likelihood of successful recrystallization.

2. Low solubility of the solute at a lower temperature: The solute should have low solubility in the chosen solvent at a lower temperature to encourage crystallization. When the solution is cooled, the solute should come out of solution as crystals, allowing for purification.

3. Selectivity: The solvent should preferentially dissolve the desired compound over impurities. This selectivity aids in the separation of the target molecule from other impurities present in the mixture.

4. Minimal chemical reactivity: The solvent should not react with the solute or any impurities in the mixture. Chemical reactions between the solvent and the solute or impurities could lead to side reactions and the formation of undesirable products.

5. Non-toxicity: The solvent should not pose any health risks to the experimenter or the environment.

6. Easy removal: The solvent should be easily removed from the purified crystals, either by evaporation or by filtration, leaving behind pure crystals.

By considering these characteristics, you can select an appropriate solvent for your recrystallization experiment that will help achieve the purification and isolation of your desired compound.