After filtration, what is the next step in the six-step preparation process?

• A. Filtrate is gently evaporated (water bath)
• B. Crystals are formed immediately
• C. Add more solvent
• D. Cool rapidly to crystallise

Answer: (A)

After filtration, the liquid that passes through the filter still contains dissolved solute. The next step is to gently evaporate the filtrate to concentrate the solution. By removing solvent slowly, the solution becomes saturated, which is when crystals start to form as the solute can no longer stay dissolved. Using a gentle heat source (like a water bath) helps control the rate so crystals form cleanly rather than boiling off too quickly.

Cooling later can promote crystallization further, but this step needs the solution to be concentrated first. The other options don’t fit because forming crystals immediately isn’t guaranteed without concentration, adding more solvent would prevent crystallization, and cooling rapidly is typically done after concentration to control crystal quality.