Differentiation of formaldehyde from other higher aldehydes

Chemicals needed

formaldehyde solution 1%   Xn    R 40-43    S 23-37

fuchsin sulphuric acid  Xi    R 36/37/38    S 26-36

propanal  F Xi   R 11-36/37/38     S (2)-9-16-29

hydrochloric acid 7%

One can also use other higher aldehydes.

Equipment needed

2 test tubes

Test procedure

• One adds to both test tubes 4-5 drops fuchsin sulphuric acid.
• In one test tube one adds a drop of propanal, in the other a drop of formalin 1%. In each tube a violet color results.
• Now one adds 2 ml diluted hydrochloric acid to each. The color of the formaldehyde soon becomes more intense, that of the propanal becomes much paler and bluish.

Disposal

The diluted mixtures can be discharged into the drainage.

Elucidation

to be possibly added

Photos

The color of formaldehyde (left) becomes more intense, that of propanal(right) pales.

Literature

derived from experiment 271, "Unterscheidung von Methanal (Formaldehyd) und Ethanal (Acetaldehyd)", p. 164, [1]