Micro-chemical test for ammonia

Author: Christine Bläuer

back to Micro-chemical testing

For more information on the required equipment and materials see the Micro-chemistry article.

Principle

When dissolving a salt containing ammonium in an alkaline 2M NaOH solution, gaseous ammonia (NH₃) is liberated which has a typical odor and will change the color of a previously wetted yellow pH indicator paper to green or blue.

Procedure

Add a drop of 2M sodium hydroxide, i.e., cautic soda, to a drop of the sample solution and immediately hold a wetted pH indicator paper directly above it into the released vapors.

or

put drop of sodium hydroxide solution (2M )on an object slide and then put one grain of the salt into it. Hold a wetted pH indicator paper directly above the preparation into the liberated vapors, while the salt is still dissolving.

Indications from the pH-value of the salt solution The pH value of an aqueous solution of nitrammite [NH₄,K (NO₃)], (also known as gwihabaite) is slightly acidic (circa pH 5). If the sample solution is acidic this is no proof for the presence of ammonium nitrate but it is a first indication