Why might crystals be dried with filter paper instead of heating?

• A. To prevent the complete loss of water from crystals and to prevent crystals from breaking
• B. To speed up drying
• C. To remove impurities
• D. To change crystal size

Answer: (A)

Drying hydrated crystals with filter paper is about keeping the water that is chemically bound inside the crystal lattice. Some crystals contain water of crystallization, so removing that water by heating would change the substance from a hydrated form to an anhydrous form and can also stress or crack the crystal as it loses water. Blotting with filter paper removes surface moisture but leaves the internal water intact, so the crystals stay intact and still hydrated. For example, copper sulfate pentahydrate is blue when hydrated, but if heated it loses water and becomes a white, anhydrous form. The other options don’t address preserving the water in the crystal or the crystal’s integrity in the same way.