Crystallization — Growing Perfect Crystals
8 experiments
Crystallization experiments teach purification and crystal growth — fundamental skills in chemistry, materials science, and geology. Controlled crystallization produces pure, well-ordered solids from solutions or melts. Students observe how temperature, concentration, cooling rate, and seed crystals affect crystal size, shape, and purity.
Learning Objectives
Understand solubility curves, supersaturation, nucleation vs. crystal growth, and how impurities affect crystal morphology. Learn to determine purity by melting point comparison. Connect crystal structure to lattice geometry and the seven crystal systems.
Key Techniques
Dissolve the solute in minimum hot solvent, filter to remove insoluble impurities, then cool slowly for large crystals or rapidly for small ones. Seed crystals initiate controlled growth. Vacuum filtration with a Buchner funnel collects crystals efficiently. Recrystallization is repeated if the melting point is not sharp.
Equipment Overview
Required: beakers, hot plate with magnetic stirrer, Buchner funnel and flask, vacuum pump, filter paper, melting point apparatus, thermometer. For advanced crystal growth: temperature-controlled water baths, string or wire frames for seed suspension.
Alum Crystal Growing
Creating large transparent alum crystals
Grow large, transparent octahedral potassium alum crystals from a supersaturated solution.
Bismuth Rainbow Crystal Growing
Creating iridescent hopper crystals from molten bismuth
Grow iridescent bismuth hopper crystals by melting bismuth metal and controlling the cooling rate to form geometric staircase structures.
Crystallization of Salol (Phenyl Salicylate)
Observing crystal growth under a microscope in real time
Observe the real-time growth of salol crystals under a microscope, studying nucleation, crystal growth rates, and the effect of temperature …
Fractional Crystallization of Salt and Sand
Separating a mixture using solubility differences
Separate a mixture of salt and sand using fractional crystallization, demonstrating dissolution, filtration, and evaporative crystallization.
Growing Copper Sulfate Crystals
Producing large blue crystals by slow evaporation
Grow large, well-formed copper sulfate pentahydrate crystals using the slow evaporation method, demonstrating supersaturation and crystal lattice formation.
Recrystallization of Benzoic Acid
Purifying a solid by dissolving in hot solvent and cooling
Purify impure benzoic acid by recrystallization from hot water, demonstrating the standard purification technique for organic solids.
Sugar Crystal Rock Candy
Growing edible sugar crystals on a string
Grow large sugar (sucrose) crystals on a string to create rock candy, demonstrating supersaturation and nucleation with an edible product.
Supersaturation and Instant Crystallization
Triggering instant crystal formation in sodium acetate
Prepare a supersaturated sodium acetate solution and trigger instantaneous crystallization, demonstrating metastable supersaturation and exothermic crystallization (hot ice).