Crystallization of Sodium Acetate

A hot, concentrated solution of sodium acetate trihydrate is cooled quietly to create a supersaturated liquid. When poured onto seed crystals, it crystallizes instantly to build a warm, solid tower.

1. Prepare a hot water bath in a large beaker or pot and heat it on a hot plate.
2. In a clean, scratch-free Erlenmeyer flask, combine sodium acetate trihydrate with a small volume of distilled water (about 3.5 g solid per mL water is typical).
3. Warm the flask in the water bath and swirl occasionally until all solid dissolves and the solution is clear.
4. Cover the flask opening with an inverted small beaker to reduce dust and allow the solution to cool undisturbed to room temperature; do not bump or shake it.
5. Place a few sodium acetate trihydrate crystals in a small beaker to act as seeds; set this beaker on a tray to contain any overflow.
6. Remove the supersaturated solution from its cover and, without jarring it, pour the liquid in a steady stream onto the seed crystals so the growing solid stays confined to the beaker.
7. Observe rapid crystallization and the formation of a white, solid column; invite students to feel the outside of the beaker to note warmth.
8. After the show, break the solid into pieces, return it to the flask with a little water, and reheat in the water bath to redissolve for reuse.

Supersaturated Solutions - Working with Sodium Acetate - Jeremy Krug (krugslist):

Sodium Acetate Crystals: Supersaturated Solution - North Carolina School of Science and Mathematics:

📄 Crystallization from a Supersaturated Solution - Rutgers-New Brunswick School of Arts and Sciences: https://chem.rutgers.edu/cldf-demos/1031-cldf-demo-crystallization

• Add a thermometer or temperature probe to quantify the temperature rise during crystallization.
• Compare seeding methods: a single crystal, a dusting of powder, or touching the surface with a glass rod dipped in crystals.
• Explore how cooling rate or storage time affects stability before seeding.

• Wear safety glasses and heat-resistant gloves when handling hot solutions and glassware.
• Keep faces and hands away from steam and hot plates; assume the beaker and solution are hot.
• Do not touch or taste any chemicals; wash hands after the demonstration.
• Pour in a continuous stream; avoid slow dribbling that can cause premature solidification at the flask neck.
• Keep liquids and hot equipment on a stable, heat-safe surface with spill containment.
• For cleanup, allow glassware to cool before washing; small quantities of sodium acetate solution are typically sink-disposable with plenty of water, following local regulations.

• Why does a cooled solution stay liquid until it touches seed crystals? (It is supersaturated and needs a nucleation site to start crystallizing.)
• Why does the solid feel warm even though the liquid started at room temperature? (Crystallization releases heat as ions organize into the crystal lattice.)
• What role does the trihydrate play compared to anhydrous sodium acetate? (At room temperature the trihydrate is the stable phase, so seeding with the trihydrate promotes rapid formation of that solid.)
• Why must the solution cool without being disturbed? (Vibration or contamination can trigger premature nucleation and spoil the supersaturated state.)
• How could adding a little extra water change the demonstration after many reuses? (It compensates for evaporation so the composition returns to the range that makes stable supersaturated solutions.)
• What determines the shape of the growing column? (The pour rate, pour position, and where new crystals contact the stream control where growth occurs.)