T515: Endothermic Reaction - Ba(OH)2 + NH4NO3

Introduction

Two dry solids --- barium hydroxide and ammonium nitrate --- are mixed to produce an endothermic reaction.  The temperature of the mixture drops approximately 45oC and is cold enough to freeze the reaction beaker to water on a block of wood

Equations

Ba(OH)2.8H2O(s) + 2NH4NO3(s)   →   Ba(NO3)2(aq) +  2NH3(aq) + 10H2O(l)

To Conduct Demonstration

1. • Mix the two solids together in a 250mL beaker.  Stir for a few seconds with a stirring rod.  (Do not stir with the thermometer.)  The mixture should become moist from the water released by the Ba(OH)2.8H2O.  DO NOT ADD ANY WATER TO THE BEAKER.
   • Place a drop or two of water on the wooden block.  Place the container on top of the block of wood, covering the water.
   • Place the thermometer in the beaker.
   • The mixture will become extremely cold and freeze the reaction beaker to the damp block of wood.  The entire block can be lifted up by lifting the beaker.
   • This reaction releases NH3 gas.  Students may be able to detect the odor if they are close enough.
   • Read the final temperature from the thermometer. 

Demo Time: 10 – 15  minutes

Safety and Disposal

Barium salts are toxic.  Avoid inhaling ammonia vapors.

Dispose of waste in the barium waste carboy or the heavy metals waste carboy.

References

Shakhashiri, B.Z. Chemical Demonstrations:  A Handbook for Teachers of Chemistry; 1983.

Acknowledgment

Margaret Asirvatham, Spring 1987.