Which of these can be used to remove colored impurities during the recrystallization process?

4. Which of these can be used to remove colored impurities during the recrystallization process?
C. Norit
Norit is a brand name for activated charcoal, which is commonly used as an adsorbent to remove colored impurities from solutions during recrystallization.

5. Why is it necessary to remove the stopper from a separatory funnel when the liquid is drained through the stopcock? To _____
D. prevent the formation of a vacuum
Removing the stopper allows air to enter the separatory funnel, preventing a vacuum from forming above the liquid as it drains. This ensures a smooth and continuous flow of liquid.

6. Which of these visualizing techniques is non-destructive?
B. UV detection
UV detection is a non-destructive method because it relies on the compound's ability to absorb UV light or fluoresce, without chemically altering the compound itself. Concentrated H₂SO₄ and Ninhydrin are destructive as they react chemically with the compounds.

7. The boiling point of a compound does not depend upon the _____
D. Solubility of the compound in water
The boiling point of a compound depends on the strength of its intermolecular forces (like hydrogen bonding, dipole-dipole interactions, and London dispersion forces), which are influenced by factors such as molecular size and polarity. Solubility in water describes how a compound interacts with water, not the energy required to overcome its own intermolecular forces to change from liquid to gas.

8. Fractionating columns are used when the _____
C. boiling point difference of the composition is less than 5°C
Fractionating columns are used in fractional distillation to separate liquids with close boiling points, typically when the difference is less than 25°C, and often specifically for differences less than 5-10°C for effective separation.