How to Make a Supersaturated Solution With Sugar

Temperature is key to preparing a supersaturated sugar solution.

A "supersaturated" solution contains more dissolved material than it should, according to the compound's solubility. In the case of sugar, whose chemical name is "sucrose," about 211 grams will dissolve in 100 milliliters of water. The first key to preparing supersaturated solutions lies in the temperature of the water. Solubility is temperature-dependent; more sugar will dissolve in hot water than will dissolve in cold water. The second key to preparing supersaturated solutions lies in preventing the excess sugar from crystallizing (solidifying) as the solution cools. In general, rapid cooling favors the formation of supersaturated solutions, whereas slow cooling favors crystallization.

Things You'll Need

• 2 lb. sugar
• 2-qt. sauce pan
• Tablespoon
• 16-oz. drinking glass
• 8-oz. measuring cup

Instructions

1. Bring 8 oz. of water to almost boiling in a 2-qt. sauce pan. This represents about 240 milliliters of water, which, according to the solubility of sucrose, should be able to dissolve about 500 grams (18 oz.) of sugar.

2. Add 16 oz. (1 lb.) of sugar to the pan and stir until dissolved. Continue adding sugar to the solution about 1 oz. (2 tbsp.) at a time until no more sugar will dissolve in the hot water.

3. Transfer the solution (slowly) to a clean glass and place the glass in a freezer for about 15 minutes. If any undissolved sugar is present in the sauce pan, be sure not to transfer it into the glass; any crystalline sugar provides a "seed" for additional sugar to crystallize.

4. Pour the supersaturated solution into a bowl or pan containing crystalline sugar. This should induce nearly instantaneous crystallization of the sugar from the solution. Alternatively, sprinkling a few crystals of sugar into the glass containing the solution should also trigger rapid crystallization.

Tips & Warnings

• If the supersaturated solution crystallizes upon cooling (if it is a white solid when you remove it from the freezer), try using a different glass, preferably one with very smooth walls. Scratches in the glass also act as "seed" crystals to induce crystallization.

References

• Chest of Books: The Solubility of the Sugars
• Elmhurst College: Temperature and Pressure Effects on Solubility
• University of Colorado, Boulder: Crystallization--Slow Cooling vs. Rapid Cooling

Resources

• Palace of Fine Arts: Science of Cooking--What is Sugar?