Cross match (chemistry)

Positive cross match

The preliminary test for ammonium salts is referred to as a cross- test in classical analytical-inorganic chemistry and is used for the qualitative detection of ammonium ions. It is carried out by putting some solid stock with sodium hydroxide (strong base ) and a few drops of water on a watch glass , which is covered with a second watch glass.

This second watch glass was provided with a moist universal indicator paper (UIP) crosswise on the inside and outside . If the sample contains ammonium salts, the inner UIP turns blue, since the sodium hydroxide releases ammonia from the sample ( displacement reaction ):

{\ displaystyle \ mathrm {NH_ {4} ^ {+} + OH ^ {-} \ longrightarrow NH_ {3} \ uparrow + H_ {2} O}}

Ammonium ions and hydroxide ions react to form gaseous ammonia and water.

Alternatively, the ammonia gas formed can be detected by its pungent odor or by smoke formation with concentrated hydrochloric acid on a glass rod.

Individual evidence

↑ Jander • Blasius: Textbook of analytical and preparative inorganic chemistry. 16th edition, S. Hirzel Verlag Stuttgart, ISBN 978-3-7776-1388-8 .

Web links

Wikibooks: Internship Inorganic Chemistry / Ammonium # Proof by means of cross-match - learning and teaching materials

[Jander-Blasius-1] Jander • Blasius: Textbook of analytical and preparative inorganic chemistry. 16th edition, S. Hirzel Verlag Stuttgart, ISBN 978-3-7776-1388-8 .