Supercooling - the energetics of freezing

Description

Students melt sodium thiosulfate crystals, and these are then cooled to a state well below the melting point. The supercooled liquid will freeze rapidly on the addition of a crystal of sodium thiosulfate, or on stirring which seeds the crystallisation process. Temperature changes are observed throughout.

supercooling-the-energeti...



Apparatus Chemicals

Each group will need:

Test-tube (Note 1)

Test-tube holder

Stirring thermometer (-10 – 110°C) (Note 2)

Beaker (100 cm3)

Bunsen burner

Tripod and gauze

Cotton wool, small tuft to fit test-tube

Sodium thiosulfate-5-water, about 20 g

Refer to Health & Safety and Technical notes section below for additional information.

 






Students melt sodium thiosulfate crystals, and these are then cooled to a state well below the melting point. The supercooled liquid will freeze rapidly on the addition of a crystal of sodium thiosulfate, or on stirring which seeds the crystallisation process. Temperature changes are observed throughout.

ADDITIONAL INFORMATION

This is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany Practical Physics and Practical Biology .