Why would crystals be dried on filter paper rather than heated?

• A. To prevent the complete loss of water from the crystals and to prevent cracking.
• B. They speed up drying.
• C. They remove impurities.
• D. They change the color.

Answer: (A)

Crystalline compounds are often hydrated, with water incorporated into the crystal structure. If you heat them to dry, you can drive off this water of crystallization, altering the composition and possibly the crystal form. This can also cause stress as the lattice loses water, leading to cracking. Drying on filter paper lets only surface moisture be removed gently at room temperature, preserving the water in the lattice and keeping the crystals intact. The other ideas don’t fit: heating would speed up drying rather than prevent changes to the crystal, drying doesn’t remove impurities by itself, and it doesn’t purposefully change color.