Recrystallization

Recrystallization is a technique for purifying solids by dissolving them in a solvent at high temperatures and then cooling to form purer crystals. The process involves selecting a solvent where the solid is insoluble at room temperature but soluble at high temperatures. After dissolution, cooling allows pure crystals to form, leaving impurities in solution. Seeding can aid crystallization. The final product's purity is tested by melting point analysis. The key is choosing the right solvent and understanding the solubility of impurities.

What is the main issue with solid precipitates formed during chemical reactions?

• They are always pure.

• They contain impurities.

• They dissolve easily.

• They are unstable.

Which characteristic is crucial for the solvent used in recrystallization?

• High solubility at room temperature and low solubility at high temperatures.

• Low solubility at high temperatures.

• High solubility at all temperatures.

• Low solubility at room temperature and high solubility at high temperatures.

What is the purpose of using a seed crystal during recrystallization?

• To dissolve impurities.

• To provide a surface for ions to coordinate and initiate crystallization.

• To increase the temperature of the solution.

• To change the color of the solution.

What is the role of an ice bath in the recrystallization process?

• To cool the solution and promote crystal formation.

• To heat the solution.

• To dissolve the solid further.

• To maintain the solution at room temperature.

How can you test the purity of the recrystallized solid?

• By tasting it.

• By observing its solubility in water.

• By measuring its melting point range.

• By checking its color.

What happens to impurities during the recrystallization process?

• They change the color of the crystals.

• They remain in solution or are filtered out.

• They evaporate with the solvent.

• They become part of the crystal lattice.

Why is it important to choose the correct solvent for recrystallization?

• To allow the solid to dissolve and recrystallize with minimal impurities.

• To change the color of the solution.

• To increase the boiling point of the solution.

• To ensure the solid remains dissolved at all times.