OC-EXP 3 Recrystallization and Decoloration

What is a desirable property of a solvent for crystallization?

• Reacts chemically with the solute

• Dissolves the solute readily at room temperature

• Is non-volatile to ensure stability

• Dissolves the solute readily at elevated temperature, but only sparingly at room temperature

Which of the following is NOT a stage in crystallization?

• Nucleus formation

• Growth of crystals to visible form

• Removal of impurities

• Evaporation of the solvent

What is the purpose of decolorizing carbon in crystallization?

• It helps in crystallization induction

• It increases the solubility of the solute

• It removes colored impurities by adsorption

• It acts as a catalyst for crystallization reaction

When should decolorizing carbon be added in the crystallization process?

• After filtration

• Before filtration while the solution is hot

• After the solution has cooled down

• It is not necessary to add decolorizing carbon

What is the purpose of "seeding" in crystallization?

• To increase impurity content

• To prevent crystal growth

• To induce crystallization process

• To slow down the cooling process

How can crystal growth be induced by scratching the container?

• By providing a smooth surface for crystal formation

• By providing a rough surface for crystal formation

• By increasing the temperature

• By adding more solvent

How does stirring or agitation affect crystal growth?

• It inhibits crystal growth

• It accelerates crystal growth

• It has no effect on crystal growth

• It decreases solubility of the solute

What effect does abrupt cooling have on crystal size?

• It produces larger crystals

• It produces smaller crystals

• It has no effect on crystal size

• It prevents crystal formation

What method is used to determine the quality of crystals obtained from crystallization?

• Melting point determination

• Boiling point determination

• Solubility test

• Color intensity measurement

When might re-crystallization with fresh solvent be necessary?

• If crystals are too small

• If crystals are too large

• If there are still impurities present

• If the temperature is too high