Cooling baths are very useful in chemistry labs to control exotherimc reactions. In this resource we share various recipes for making cooling baths to temperatures below 0°C.

There are many instances where you will need cooling as part of the procedure, for example in recrystallisation, carrying out reactions at low temperatures, controlling exothermic reactions as well as in vapour traps.

Coolant

Temperature            

Comments

Ice Bath

0 - 5°C

It is important to have a crushed ice - water mixture to ensure good conduction.

Crushed Ice - CaCl2.6H2 O (2.5:1)

-10°C 

These baths are ‘dry’ mixtures and so conduction of heat away from a vessel will be inefficient.

Crushed Ice - NaCl (3:1)

-20°C 

Crushed Ice - CaCl2.6H2 O (0.8:1)

-40°C 

Dry Ice - Acetone (propanone)

-78°C 

Dry ice can cause severe frostbite if it comes in contact with bare skin so insulating gloves should always be worn. The baths should be made up with small pieces of dry ice and topped up with further dry ice periodically.

Liquid Nitrogen

-196°C  

Liquid Nitrogen is a hazardous material that can cause severe frostbite in contact with bare skin so insulating gloves should always be worn. Because of the risk of suffocation liquid nitrogen should only be used in well ventilated areas.

 

 

Additional information

The Interactive lab primer has been developed as part of the Royal Society of Chemistry Teacher Fellowship Scheme titled ‘Chemistry for our Future’ in partnership with the University of Southampton, The University of Nottingham, University of Birmingham and The University of Sheffield

© Royal Society of Chemistry

This resource is part of the interactive lab primer collection.