Super Saturated Sodium Acetate

DESCRIPTION:
A super saturated sodium acetate solution is poured onto a sodium acetate seed crystal. The seed crystal provides a crystalline structure template for the sodium acetate ions to form on. This is an exothermic process.

TOPICS COVERED:
exothermic reactions
super saturation
solubility

MATERIALS NEEDED:
– 175g of NaC2H3O2 ∙ 3H2O
– 50mL of water
– hot plate
– stir rod
– crystallizing dish
– 250mL beaker

PROCEDURE:
1. Add the sodium acetate and water to the 250mL beaker
2. Place the beaker on the hot plate, and heat it on medium heat
3. When all of the solid has gone into solution, turn the heat off and let the beaker cool on the hot plate (this takes a few hours)
4. Add a few granules of sodium acetate to the crystallizing dish
5. Slowly pour the sodium acetate solution onto the granules, it should quickly turn white and solidify

ADDITIONAL COMMENTS:
This demo can be very finicky, but it is worth and frustration it causes. The sodium acetate can be saved by storing it in a covered beaker. It will need to be re-melted for the next demo, but be careful, if there is any sodium acetate at all on the pouring spout of the beaker the solution will solidify in the beaker when you go to pour it.

SAFETY:
Safety goggles should be worn at all times and caution should be taken with a hot beaker.

REFERENCES:
Shakhashiri, B.Z. Chemical Demonstrations;  University of Wisconsin Press: Madison, 1983; Vol. 1, pp 27-31.

“Crystallization of Supersaturated Sodium Acetate” Chemistry Comes Alive! Web. 21 Feb 2012.
http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA3/MAIN/ACETATE/PAGE1.HTM

Handout