Verification of sulfite with formaldehyde


Chemicals needed

distilled water

formaldehyde solution 1% GSGESUND.gif (476 Byte) Xn    R 40-43    S 23-37

sodium sulphite GSGESUND.gif (476 Byte) Xi    R 31

phenolphtalein solution

hydrochloric acid 7%

it is basically advantageous to use still less concentrated acids


Equipment needed

test tube


Test procedure


Disposal

The diluted solution can be disposed of into the drainage.

Elucidation

Sodium hydroxymethyl sulfite(bisulfite adduct) and sodium hydroxide are formed. The latter is strongly alkaline and therefore causes the indicator to change.

HCHO + H2O +  Na2SO3 --> HOCH2OSOO- + 2 Na+ + OH-


Photos

Dropwise added formaldehyde solution causes the indicator to change.


Literature

Derived from experiment 6.,"Nachweis mit Formaldehyd", p.122,[7]