I performed an extraction of caffeine from tea/coffee experiment and in of the last steps where I added a drying agent (Sodium Sulphate) into the DCM solution (containing caffeine after extraction and filtering), there were really cold crystals formed on the filter paper. Why did it happen and what was the cause of it?
To purify caffeine as much as possible, anhydrous sodium sulfate is added. Anhydrous compounds are substances that lack water of crystallization, thus absorbing water to create crystals of itself. Thus, when enough of anhydrous sodium sulfate is added to the solution, the salt crystallizes by absorbing the water in the solution, leaving the solution free of water, isolating caffeine.