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.)

  1. 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.

  1. Boil any flasks containing crystallized NaOAc until solid is dissolved.
  2. Assemble the following:
  •   Small amount of solid sodium acetate
  •   Small board or flat piece of plastic

To Conduct Demonstration

  1. 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

  1. 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