Verification of aluminium with alizarin

Chemicals needed

aluminium sulphate

acetic acid 25% C     R 10-35    S (1/2)-23-26-45

ethanolic alizarin solution  F    R 11    S (2)-7-16

Equipment needed

test tube

Test procedure

• One adds a spatula-tipful of aluminium sulphate into a test tube and dissolves this with approx. 1 ml of acetic acid 25%.
• One adds 4-5 drops of alizarin solution.
• After a while the reaction mixture clarifies and takes on a reddish color.

Disposal

• The diluted solution can be disposed of in the drainage.

Elucidation

Alizarin forms with aluminium(III) a colored complex. Alizarin (derived from madder root) + alum (potassium aluminum sulfate) was in the past very important for the dyeing of fabrics.

Structural formula of alizarin

Photos

Alizarin aluminium complex (left), alizarin solution (right)

Literature

Inspired by VII.3, "Aluminiumnachweis als Alizarin-S-Farblack", p. 76, [3]
see under: Al-Nachweis mit Alizarinsulfonsäure, Natriumsalz