Question

1. Water is the best choice for use as a crystallization solvent whenever possible. Why?

2. Why do you crystallize your product as slowly as possible?

3. Why would n-propyl alcohol, CH3CH2CH2OH be more soluble in water than n-propyl bromide, CH3CH2CH2Br?

Answer 1

1).

Crystallization is the technique in which impure substance is dissolved in the solvent. The condition for it is the substance should be dissolved in the solvent. With many of the impurities should be dissolved in the solvent. And we know, water is called as universal solvent since it can many substance in it. So water is the best choice.

2).

Crystallization is the process to form a crystal from the substance which is dissolved in the solvent.

If we allow it to crystallize suddenly then there may the chance of trapping impurity between crystal.

And when we allow it slowly then in impurities do not involved in the crystal.

3).

Here n-propyl alcohol and n-propyl bromide both are polar but the solubility of n-propyl in water is more in water due to formation of H-bonding.

H-bonding : This is the electrostatic attraction between H bonded to the more electronegative element like F , O or N ,etc. and more negative element.

H of alcohol group can form bond with oxygen of water and H of water group can form bond with Oxygen of alcoholic group. This makes extra solubility.

Lets show the formation of H bonding: