When drying crystals, which method is recommended to minimize water loss and preserve crystal integrity?

• A. Heating
• B. Drying on filter paper
• C. Dissolving and re-precipitating
• D. Grinding

Answer: (B)

Drying crystals without losing their water content or damaging their shape is about removing only surface moisture gently while keeping the internal water bound in the crystal structure. Drying on filter paper does this well—the crystals sit on an absorbent surface and surface water is drawn away gradually by capillary action into the paper, so the crystals stay intact and their hydration state is preserved if they are hydrates. No heat is used, so water of crystallization isn’t driven off and the crystal lattice isn’t stressed or altered. Heating would remove water more aggressively and could dehydration-change the material; dissolving and re-precipitating would require dissolving the crystals and then recrystallizing, which can alter shape, purity, and hydration; grinding would physically break the crystals and change their size and structure.