when is it better to use recrystallization vs. sublimation techniques in lab? I know they both result a purer compound, but I am confused on when one technique is better than the other.
I don't think its a matter of what is better but which is more convenient. For example, one material may be much more volatile than the other or you may have trouble finding the proper solvent but sublimation doesn't have that problem.
Recrystallization and sublimation are both techniques used for purification of compounds in the laboratory, but they are applied in different scenarios depending on the compound and its specific properties.
Recrystallization involves dissolving a solid compound in a hot solvent, allowing it to slowly cool down, and then collecting the purified solid crystals that form. This technique is most commonly used when the compound you are working with is relatively insoluble or only sparingly soluble in a cold solvent, but highly soluble in a hot solvent. The solid impurities, which have different solubilities, generally remain in the solution and are later discarded. Recrystallization is effective for removing soluble impurities, such as organic or inorganic contaminants, from the compound.
On the other hand, sublimation is a technique used for purifying compounds that can undergo sublimation, the process of transitioning directly from a solid to a vapor without passing through a liquid phase. Sublimation is typically conducted at low pressures and temperatures, where the compound directly evaporates and then recondenses to form pure crystals. The impurities, which typically have lower sublimation temperatures or different chemical properties, are left behind. Sublimation is particularly useful for compounds that are volatile and thermally stable, with a significant vapor pressure at a given temperature.
So, in summary, recrystallization is generally more suitable for compounds that are relatively insoluble or sparingly soluble in a cold solvent and can be dissolved in a hot solvent, while sublimation is better for compounds that can undergo sublimation at low pressures and temperatures. The choice between the two techniques ultimately depends on the properties of the compound you are trying to purify and the available solvents and equipment in the laboratory.