S150: Prep Notes
Introduction
A seed crystal can be dropped into a saturated solution of sodium acetate. The solution will suddenly crystallize and turn to solid. Alternately, the solution may be slowly poured out onto a seed crystal on a flat surface. The solution will crystallize as it touches the crystal, resulting in an increasingly tall tower of sodium acetate.
NaC2H3O2(aq) → NaC2H3O2 • xH2O(s) + ∆
Supplies
Short List
- H2O
- 100 mL beaker
- 50 mL Erlenmeyer
- Hot plate
- Crystallizing dish
Chemicals
- NaOAc
Prior to Lecture (prep time ~ ? min.)
- Prepare several saturated sodium acetate (NaOAc) solutions:
Mix 175g of NaOAc trihydrate with 50mL distilled water in a very clean 500mL erlenmeyer flask and heat in a boiling water bath until all solid is dissolved. Remove from bath, rinse down sides with tiny amount of distilled water, and allow to cool. Invert a clean 100mL beaker over the top of the beaker.
- Boil any flasks containing crystallized NaOAc until solid is dissolved.
- Assemble the following:
- Small amount of solid sodium acetate
- Small board or flat piece of plastic
To Conduct Demonstration
Carefully drop a seed crystal into a flask of saturated sodium acetate. Solution will immediately crystallize into a solid and give off a large quantity of heat.
Or
- Place a seed crystal of sodium acetate on a board or flat piece of plastic. Slowly pour saturated sodium acetate solution onto the crystal. A tower of crystallized sodium acetate will grow upwards.
Note: Please be aware that, even with the greatest care, saturated sodium acetate solutions are prone to crystallize spontaneously. The farther the flasks are carried, the greater the risk.
Demo Time: ~? minutes
Safety
Dispose in the appropriate waste container