Which characteristic does NOT describe a good recrystallization solvent.
Select one:
O a. Solvent dissolves product at high temperatures
O b. Does not dissolve impurities
O c. Solvent with high boiling points
The Correct Answer and Explanation is:
Correct Answer:
✅ c. Solvent with high boiling points
Recrystallization is a widely used technique in chemistry for purifying solid compounds. The effectiveness of this process heavily relies on the choice of solvent. A good recrystallization solvent must exhibit certain characteristics to ensure optimal purification.
Let’s break down the options:
a. Solvent dissolves product at high temperatures
✔️ This is a desired property. A good recrystallization solvent should dissolve a large amount of the solute when hot but only a small amount when cold. This temperature-dependent solubility allows the solute to recrystallize upon cooling, leaving impurities in the solution.
b. Does not dissolve impurities
✔️ Also a desired property. A good solvent should either not dissolve impurities at all or keep them soluble at all temperatures. This ensures that impurities are either filtered out before recrystallization or remain dissolved in the solvent and do not contaminate the crystals.
c. Solvent with high boiling points
❌ This is NOT a desirable characteristic. High-boiling-point solvents can be problematic for recrystallization. Here’s why:
- Difficult to remove: Solvents with high boiling points evaporate slowly, making it harder to dry the purified crystals.
- Decomposition risk: Prolonged heating at high temperatures may lead to decomposition of the solute or formation of side products.
- Safety concerns: High-boiling solvents often require more energy to heat and can pose safety risks in the lab.
Instead, ideal solvents should have moderate boiling points, allowing them to be heated easily during the dissolution process and evaporated efficiently afterward.
Conclusion:
While solubility behavior and interaction with impurities are essential factors, the boiling point plays a critical practical role. Therefore, option (c) is the correct answer, as high boiling point is not a characteristic of a good recrystallization solvent.
