Demonstration of orange II

Chemicals needed

distilled water

2-naphthol Xn   N    R 20/22-50     S (2)-24/25-61

sodium nitrite solution, diluted Xn  N    R 8-25-50    S (1/2)-45-61

sulfanilic acid Xi     R 36/38-43    S (2)-24-37

Equipment needed

test tube

Test procedure

• In a test tube add a spatula-tipful 2-naphthol and a spatula-tipful sulfanilic acid.
• Create a suspension with approx. 4 ml distilled water.
• Add a couple of drops of sodium nitrite solution. The color of the mixture turns at first to yellow, then to orange and finally to red. This can possibly take several minutes, the ingredients partially dissolve. If one adds lye the transformation is dramatically accelerated, but without it is much more beautiful to observe.

Disposal

The mixture can be disposed of as halogen-free organic waste.

Elucidation

This experiment corresponds to the usual procedure for the demonstration of azo dyes. Orange II has the following structure:

Orange II - 4-[(2-Hydroxy-1-naphtyl)azo]-benzenesulfonic acid monosodium salt

Photos

With neutral conditions the coloration develops in the course of several minutes

Literature

based on experiment 2058 S "Orange II", S. 334, [2]